So I played around with this this morning and I was able to make an enemy use the attack I wanted, I made it use the unused attack EC: then I changed the graphics of that attack to the ones I wanted.
So far so good. Unfortunately I couldn't make it attack other enemies despite my new tech meeting the conditions ( Enemy vs Enemy:True, and targeting One Ally 0x00)
The last bit you posted didn't seem to do anything, do I use exclusively that or in addition to what's there? Also do I give that to the other enemies that are with the guest or the guest itself? For now I'm just using enemy E7.
As for Barrier if I had to guess and I'm a terrible guesser I think it has problems with status effect that have the glow effect, even if they come from another piece of equipment.