1. velocity - there's only 3 to choose from (none of them are what most people use by default) and the velocity shift button for single notes already exists. if you wanted to change the constant velocity, it's easily done with the velocity plugin or editing the script.
2. mute shift - there's already a mute lane mode which is much easier to use.
maybe you could replace these two buttons with a page-up/page-down?

oh and one more thing: if notes longer than their quantization could light up multiple LED buttons, but only if the spot is taken up fully. for example, in 1/4 note quantization, a dotted 1/4 note (1/4 + 1/8 = 3/8 in length) would not take up 2 LED buttons because it does not occupy the 2nd button fully, while a 1/2 note would take up 2 buttons.