Using
WHFB models in
WH40K and throwing in some lasguns and autocannons? That is SO not original.
Maybe you could add cyborg parts to flagellants

and have them go as repenting cannon fodder. Never been too happy with this faith in the EMPEROR OF *cough* MANKIND *cough cough* and twisted demons from the warp hell thing. Sounds too much like an ecclesiarch's nightmare in the 15th century. Back then you just got up and counted the coins you reaped from fanatacized pilgrims, in
40k you get to unload a boltgun at real daemons

!