Your talking puttin a vert foregrip reg in place of a gas thru/ grip? If that's what your doing than, I don't think so, as long as there's some form of pressure regulation between the asa and the point where air enters the body you should be fine.
I replaced a gas thru with a tribal shocker reg on a freak factory instead of usin the horizontal max flo it used to have. If your talkin about mounting you MAY need a vertival reg adapter, and that's a big MAY. I'm not sure how old your talkin about