General statline buffs:

All Custodes infantry and bikes get +1 wound and +1 attack. This seems in line with alle the buffs going around in the 9th ed codices. Other than that, there is not much you can change on their statline, since it's already pretty premium, though especially the extra wound feels needed.

Note that these general buffs hinge on the assumption that custodes retain their inherent 4+ invuln and 3+ invuln exclusively on their storm shields. If they lose their 3+ invuln on storm shields as their "gimmick" they need something else to make up for it, like you can't re-roll hits and/or wounds against custodes with storm shields.


Weapon upgrades:
Note that I would leave the shooting profiles of the weapons untouched. I think they are fine, though one can argue that the spears and axes should be changes to assault 3 or something along those lines.


-Sentinel Blade:

S:+1, AP-3, Dmg D3
Every time the bearer uses this weapon in the fight phase, he can make one additional attack with this weapon

-Guardian Spear:
Auric Blade Barrier: whenever an enemy model makes a melee attack against this unit, any model equipped with a guardian spear can attempt to block ONE incoming enemy attack. Chose one enemy hit roll made against this unit for every model attempting to block an attack. Roll one D6 for each attempt to block, if the roll exceeds your opponents hit roll the attack is blocked and has no effect.
Two or more friendly models equipped with guardian spears can attempt to block one attack together, if you chose to do this, roll one additional D6 for every model attempting to assist in blocking an enemy attack, if the value exceeds your opponents hit roll, the attack is blocked and has no effect. (Disclaimer: basically the 7th ed block rule)

Every time the bearer fights with this weapon, at the beginning of the fight phase chose one of the following profiles to use in the fight phase:

Sweeping Strike: S: User, AP -2, Dmg 1
Every time the bearer uses the sweeping strike profile of this weapon, double the attacks characteristic of this units profile.

Piercing Strike: S:+2, AP -3, Dmg 2

-[u]Castellan Axe:
S:+3, AP -2, Dmg 3

-Interceptor Lance:
S:+1, AP -3, Dmg D3
Whenever a model equipped with this weapon finishes a charge move, change the weapon profile to: S:+1, AP -3, Dmg 3. In addition, every time a model equipped with an interceptor lance finishes a charge move, you can re-roll the wound roll.

Watchers Axe (Trajann Valoris' Axe)
S: x2, AP -4, Dmg 4


Shield Hosts:
If your army detachment is battleforged you can chose one of the following shield hosts. Every >Adeptus Custodes< unit in your detachment gains the keyword of the chosen Shield Host.

-Dread Host:
Cold Aggression: Every time an >Adeptus Custodes< unit with the >Dread Host< keyword finishes a charge move, that unit gains +1Strength and +1Attack until the end of the fight phase.

Warlord Trait:
All-Seeing Annihilator:
-Whenever an >Adeptus Custodes< >Dreadhost< unit within 6" of this warlord rolls an unmodified 6 in the fight phase, that attack generates one extra hit.
-Whenever your warlord scores an unmodified wound roll of 6, that attack does one mortal wound in addition to any other damage.

Relic:
Admonimortis: replaces the bearers castellan axe
S: x2, AP -3: Dmg 3
Whenever the bearer finishes a charge move roll one D6, on a 2+ the enemy unit suffers D3 mortal wounds.

Dreadhost Strat:
Golden Light of the Moraides(1CP/2CP): unchanged.


-Shadowkeepers:
Jailers of unspeakable Nightmares: Every enemy unit within 3" of an >Adeptus Custodes< >Shadowkeepers< unit must subtract 1 from its attack profile to a minimum of 1. Note that this rule is not cumulative if an enemy unit is within 3" of two friendly >Adeptus Custodes< >Shadowkeepers< units.

Warlord Trait:
Lockwarden:
-Whenever your warlord makes a melee attack against an enemy character, subtract 1 from that enemy characters save characteristic including invulnerable saves.
-At the start of the fight phase, choose one enemy character within 3" of your warlod. Whenever the chosen enemy character fights against your warlord, halve the enemy characters attacks (rounding up). Not that this is not cumulative with the Jailers of unspeakable Nightmares rule.

Relic:
Statis Oubilette:
Can only be used once per battle. At the start of the fight phase, choose an enemy character within 3" of the bearer, until your next turn the enemy character can not use it's invulnerable saves or any rules that ignore damage. In addition, halve the move characteristic of the enemy character until your next turn.

Shadowkeepers Strat:
Grim Responsibility (1CP): unchanged.


-Solar Watch:
Auric Wings: Add 1 to every advance and charge roll made by an >Adeptus Custodes< >Solar Watch< unit.

Warlord Trait:
Sally Forth: at the beginning of the movement phase, choose a friendly >Adeptus Custodes< >Solar Watch< unit within 6" of your warlord. That unit can attempt to charge even if it advanced this turn.

Relic:
Swiftsilver Talon: Relic Interceptor Lance
S:+1, AP: -3, Dmg 2
Whenever a model equipped with this weapon finishes a charge move, change the weapon profile to: S:+2, AP -3, Dmg 4 . In addition, every time a model equipped with an interceptor lance finishes a charge move, you can re-roll the wound roll.

Solar Watch Strat:
The Eagle's Strike (1CP):
At the end of the movement phase, select one friendly >Adeptus Custodes< >Solar Watch< unit. That unit is eligible to shoot and charge even if it fell back this turn.


-Aquilan Shield:
Shield Wall: whenever an attack is allocated to a friendly >Adeptus Custodes< >Aquilan Shield< >Infantry< unit, subtract 1 from the damage characteristic of the enemy attack to a minimum of 1.

Warlord Trait:
Revered Companion: When resolving an attack against this warlord, subtract 1 from the wound roll. In addition, enemy units can not re-roll their hit roll when resolving an attack against this warlord.

Relic:
Praesidius: Relic Storm shield (3+ invuln)
Whenever resolving an attack against this warlord, the enemy unit can not re-roll their wound roll. In addition, when resolving an attack against this warlord, halve any incoming damage rounding up. Note that this replaces the Aquilan Shield Shield Wall rule.

Aquilan Shield Strat:
Golden Bulwark (1CP/2CP):
When resolving an attack against an >Aquilan Shield< Custodian Guard unit equipped with storm shields, until the end of the phase, subtract 1 from the attacks wound roll. In addition until the end of the phase, enemy units can not re-roll their hit-roll when targeting this unit.


Standard Warlord Traits:

-Superior Creation: unchanged

-Radiant Mantle: unchanged

-Impregnable Mind: unchanged

-Peerless Warrior: This warlord always fights first in the fight phase.

-Emperor's Companion: At the start of your turn, this unit regains 1 lost wound

-Champion of the Imperium: increase the range of aura abilities of this warlord by 3"


Captain Commander Traits:

-Strategic Mastermind: unchanged

-Bane of Abominations: unchanged

-Slayer of the Unlcean: when resolving an attack made by this model, on an unmodified attack roll of 6, the attack wounds automatically and does double damage.

-Indomitable constitution: increase the toughness characteristic of this warlord by 1

-Master of Melee: at the end of the fight phase whenever this model has fought, chose one enemy unit in engangement range. That enemy unit suffers D3 mortal wounds.

-Unstoppable Destroyer: choose one enemy unit within 3" of this warlord at the beginning of the fight phase, that unit is not eligible to fight until all other units have done so.

-Inspirational Exemplar: Every friendly >Imperium< unit within 6" of this warlord can re-roll their moral and ignores combat attrition.

-Defiant to the Last: roll one D6 the first time this warlord is slain. On a 3+ this warlord returns to the battlefield with 2 D3 wounds remaining. Place this warlord at the nearest point where it was slain, but out of engagement range of enemy models.

Non Shield Host Relics:

(Disclaimer: again, this is assuming we keep the 3+ invuln as our gimmick)
-Auric Aquilas: unchanged
-Eagle's Eye: unchanged

If we lose the 3+ invuln:
-[u]Auric Aquilas: bike captain only. Whenever an attack is allocated to this unit, subtract 1 from that attacks wound roll. In addition enemies can not re-roll their wound roll when targeting this model (both melee and shooting)
-Eagle's Eye: whenever an attack is allocated to this unit, a hit-roll of 1-3 always fails.


-The Praetorian Plate: Terminator Captain only. Whenever an attack is allocated to this unit, a wound-roll of 1-3 always fails.

-Gatekeeper:
Relic Guardian Spear: Melee: S+3, AP -3, Dmg 2; Shooting: 24", Rapid Fire 3, S 5, AP -1, Dmg 2
Abilities: Overwatch hit roll hit on 3+ rather on 6+. In addition the bearer can attempt to use the "Auric Blade Barrier" rule for Guardian Spears on 3 incoming attacks instead of just one.

-The Veiled Blade:
Relic Sentinel Blade: Melee: S+1, AP -3, Dmg D3; Shooting: 12", Pistol 3, S 4, AP -1, Dmg 1
Abilities: Whenever an enemy unit within engagement range of the bearer chooses to fall back, roll one D6. On a 3+ the enemy unit can not fall back.

-Obliteratum:
Relic Balistus Grenade Launcher: Shooting: 12", Assault 1, S 10, AP-4, Dmg 3+D3

-Emperor's Light:
Relic Misericordia: Melee: S user, AP -2, Dmg 1
Abilities: Each time the bearer fights, he can make one additional attack with this weapon. Attacks made by this weapon ignore any invulnerable saves.

-Wrath Angelis:
Replaces a Vexilla Magnifica: at the beginning of the fight phase, the bearer can choose one enemy unit within 3". This unit is not eligible to fight until all other units have done so.

-Auric Shackles:
At the end of the movement phase, chose one enemy unit within 12" of the bearer. Until your next command phase, that enemy unit halves its move characteristic (rounded up).

-Fulminaris Aggressor:
Replaces Vexilla Imperius: Shooting: 12", S 5, AP-2, Dmg 1; Melee: S +2, AP -2, Dmg 1
Abilities: Attacks made with this weapons shooting profile automatically hit. In addition, at the end of the movement phase, chose one enemy unit within 6" of the bearer. That unit suffers D3 mortal wounds.

-Raiment of Sorrows:
Roll a D6 each time a friendly >Adeptus Custodes< >Infantry< or >Biker< unit within 6" of the bearer would lose a wound. On a 6+ the wound is not lost.

-The Castellan's Mark:
Once per game use only: At the beginning of the shooting phase, chose one firendly >Adeptus Custodes< >Infantry< or >Biker< unit within 6" of the bearer. This unit can move as if it were the movement phase.

-Faith Absolute:
Replaces Vexilla Defensor: Whenever a friendly >Adeptus Custodes< unit within 6" of the bearer would lose a wound as a result of a mortal wound, roll one D6. On a 4+ that wound is not lost.