BigMarlin wrote:If I create a custom guard regiment can I give them the MILITARUM TEMPESTUS regiment keyword? If I can give them the keyword, can I put them in tempestor primes?
No, you cannot. Page 84 of the codex:
Page 84 wrote:Units with the MILITARUM TEMPESTUS keyword treat this as their <REGIMENT> keyword in all respects, but the MILITARUM TEMPESTUS keyword cannot be used to replace the <REGIMENT> keyword on
any other datasheet.
However, your custom regiment can take the Storm Troopers doctrine.
If you want to include Scions, slap them in their own detachment for best effect.
Also, rules questions go in
YMDC for next time.
And even if you could, the Designers Commentary forbids you from doing what you're trying to do.
https://whc-cdn.games-workshop.com/wp-content/uploads/2017/11/warhammer_40000_designers_commentary_en-1.pdf
Q: If I create an Astra Militarum Regiment of my own and name them, for example, the ‘Emperor’s Finest’, and I then also create an Adeptus Astartes Chapter of my own choosing, and also call them the ‘Emperor’s Finest’, do the abilities that work on the <Regiment> and/or <Chapter> keywords now work on both the Astra Militarum and Adeptus Astartes units?
A: No.
The intent of naming Regiments, Chapters, etc. of your own creation is to personalise your collections and not to enable players to circumvent the restrictions on what abilities affect what units. It is also not intended to circumvent the restrictions on which units are able to be included in the same Detachment.