...well, you are the first person to actually report anything negative with the mouse fix so far. What kind of computer are you using to play srb2 then?
In any case, the mouse fix isn't something that can be just "turned off"; i basically rewrote the mouse code to rely on sdl2's relative mouse mode feature, which is supposed to change mouse input so that it doesn't actually change position but gives only the x/y movement. In other words it's supposed to stay in place. If that doesn't work somehow, it must be your computer not supporting this feature somehow (to the best of my knowledge). Best i could try to do is somehow reimplement the warping hack as an option or something, but i'm not sure how awkward that'd be to do. *shrugs*
for the record, i play srb2 with windows 7, and the mouse fix exe works just fine for me. However, i did not have the issues everyone reported in the first place either; most of those people apparently started getting it on windows 10 after getting the fall creators update thing.