mmmm for the first question, i would suggest script. Eventing...it would be possible........ but you'd basically have to set up a whole battle system using events since each turn would have to be recorded some how, mostly by variables, and then a skill would have to be linked to it recognizing specific variables to undo or erase within the battle. Complicated...
for your second question, there's probably a TBS out for XP. i don't know too much about scripts and stuff of XP anymore, i know there's a couple for VX tho. TBS, as in tactical battle system.