I can give detailed specs for the PC version, but the PSX follows different rules. Basically, you'd need to know about
relative animation indexes. Read that, then come back.
Read it yet? Then go do it... OK, now that you have let me say that I've learned a lot since I made that topic, but the basics are still true. Basically, there's a list of 322 pointers that point to animation data/routines. Each action type (Item, Magic, Summon, etc) has a list that points to one of these animation indexes. There are no bounds checking when these lists are queried so it's possible to create a memory leak into another list. Nice thing is that all these lists are right next to each other. So if we assume the bytes in the action data are relative, how can we make it look like something else? You can use this for the PC version, although Bosola may have an updated PSX list:
Action Absolute
Items 0
Magic 46
ESkill 7E
Summon 96
Enemy AA
Limit 14A
Throw 19A
So to make a magic look like an Enemy Animation you'd need to add (AA - 46), or 64h, to the animation index of the magic. This will give you access to the first 155 animations of Enemy animations to work with. Some don't like being performed by playable characters (which is what you want to know).
Bosola has made a similar topic about the PSX version which links to a document containing his findings.