Kinda surprised I haven't seen anything like this aside from that one mod that adds the two-piece to the astra mlitarum but, why hasn't anybody made a custodes faction mod or even an integration into the space marines units ala rowboat girlyman getting the thumbs up from big e on telling them to go do things again. no doubt the modelling would be WORK but, in terms of stats and what not, could just make them like, I dunno x1.35 normal space marine stats at like x1.65 the upkeep? they really only should get one or two hero units though being that, you know, they're all already kinda each their own "hero" unit lorewise. But, like, in terms of gameplay, they really only need to be slightly better golden banana marines with their spears. Vehicles would be a nightmare, thinking about it, doable but, a nightmare to model and likely implement right.

Anyway, TLDR;
Gib golden banana men. Want spear the heresy.