Is there any way in unity hdrp draw on decal vertex colour to use it as opacity mask?

Hi there! I saw decal pack on youtube recently, fantasy of Rome or something like that, and they use vertex painting on decal to make some parts of it transparent. I work in hdrp pipeline, so I can use planes as decals with hdrp decal material and decal projector, and it's awesome, but is there a way to draw in transparency of plane or projected decal using Polybrush? My goal is to use one texture to get many unique decals.