Hello!
1) By Pressing shift + 'Qnt 50%' (or 'Qnt 100%')
2) Undo works for Clr Ptn, Erase Ptn (project, page, steps, etc...), Paste Ptn -> The memory structure of KSP
3) There is no way to limit the range of random but it randomize notes within the scale yes. Also it randomize only the active steps + the steps that are within the lst step (does not randomize the one after)
Hope it helps,
Best,
Adrien