This is a late 7th ed question and I was wondering your insight into this rule.
Fall of Cadia wrote: Characters that can normally take a Relic (or equivalent) and have been selected as part of a Conclave Acquisitorius Formation, a Grand Conclave Detachment, or are in an army that includes an army that includes Belisarius Cawl, can select one of the following Arcana Mechanicum.
A Tank Commander is a Character, and if Cadian can take Kabe's Herald. The Herald is the only Relic said commander normally legally has access to however. Would this qualify the Tank Commander for access to an Admech Relic? The tenative idea would be to take Cawl for normal tank-buffing, and a Cadian Tank Commander with a Memento-Mortispex as a "budget Pask" of a sort. The Mortispex would grant the unit its choice of Skyfire, Tank Hunter, Monster Hunter or Cognis, and would be an interesting modelling project either way.