Yes, but player master grip used in isolation has an effect from the ability/variance in the performance file.
Player master grip & the other 'grip/bhp' option used together means the magic data and player master grip combine.
For example -
I set an average laptime of 1.38.9 in Melbourne (Vettel Ferarri Tom CSM 15' mod - melbourne perf file & therefore player master grip value taken from this)
This 1.38.9 was set with bhp/grip patched (top option in Belini's tool) & the player master grip (bottom option) patched to match the perf file.
The magic data was set to cc power & cc grip settings of 500 & 500.
I then adjusted the cc grip to bring the ai in line with my 1.38.9 ability before quali. This was then 500 & 457 settings (out of interest, does anyone know how much 1 point equates to in time on these settings?)
I set of for quali and MY grip was far reduced, resulting in a best time of 1.47 or something (all over the place).
I then unpatched the bhp/grip (top option in Belini's tool) and I was able to set times of 1.34 odd.
The top option must mean the magic data grip value is used for player & ai when patched and when unpatched its just the ai who are effected.
Having tried different player master grip values (bottom option), this effects only the player when used in isolation (expected results) and the ai times remain unaffected, only changing when the magic data cc grip value is adjusted.