I put KC_ACL0, KC_ACL1, KC_ACL2 on the adjust layer of my keymap. However, they do not seem to affect the mouse acceleration of the mouse controls on the keyboard whatsoever.
Are you holding those keys while pressing the mouse keys, or you just tap them and release?
Oh, so you're supposed to hold them? That would explain why they did nothing. (I tapped and released)
Yep. You can turn them into macros that keep them held until a second tap, if that's more convenient for you.
(Which is something I always wanted to do, but forgot, so I'm doing it now, thanks for the reminder! :))