Not sure I would recommend that on the flat head screws, by the looks of the grips there wouldn't be much left for the allen wrench to grab. Just have
altering screws is fast, free (if you have the tools) and leaves the grips un-altered for use on different frames in the future. also, there would be
I would just open up (deepen) the countersinks and keep the standard screws since the grips are clear/raw.
That way, any future standard #8 FHSC