Not sure if I should post this here or in the GM section.

One of my players is playing an Enginseer from the great forge world Agripina. He has no connection to the Lathes and has previously awed other tech adepts by coming from the greatest forge world in the segmentum. He wants to play a Myrmidon or other warrior tech priest. I just bought Shield of Humanity and find that the Crimson Exemplar are Lathes only. Do I have to make up house rules for his new class? Are there Crimson Exemplars elsewhere in the Adeptus Mechanicus?

Eh ... by the fluff, the Crimson Exemplars are an elite group amongst the Venatorii that were formed in the Lathes after their Skitarii forces got mauled, so strictly speaking ... no, not without a trip to the Lathes for signing on for a tour of duty with the Crimson Guard and/or Lords Dragon, probably with other requirements as well.

In the real world, however, FFG invented the Venatorii, aka, "Crimson Guard", because GW wouldn't allow them to use Skitarii for the Lathes World DH supplement (and by extension, the other game lines).

As such ... I would probably allow a sufficiently militant and appropriately backstoried/origined tech-priest to take a refluffed and relabeled equivalent of the Crimson Exemplar.