Seems like viewing object space normal maps in marmoset already works ok, so it would be really nice to get the option to paint/edit them in the painting tools. Doesn't seem like there's anyway to do that currently unless I'm missing something. At least not in a way were you can get a live preview of their effect.
Not 100% sure but i think painting on the "normals/any" is taboo last i heard and a no no do not do that, from what i read but i do agree, i'd like to do the same sometimes, but then they will just say you have bad practice or are trying to cut corners and "really" the goal should be to fix the process of the high instead…