Can a recorded loop’s tempo be varied post-recording, not affecting the pitch?
Can a recorded loop's exact start and end be tailored post-recording, in order to make it come in tighter on the footswitch push?
No, this is not possible, because time-stretching is not available with regard to VoiceLive 3's loops.
Generally speaking, there is no way to edit a loop in any way after it has been recorded. It can only be assigned to a loop Slot (10 in total) which can then be assigned to a footswitch on a given preset within VoiceLive 3.