Hey Gensis. So the short answer is yes, but there's a bit of work involved. My only experience with this was the Red Werewolf mod with Wolfman. First you have to have a skeleton for a model that fits the animations you want to use (in our case we used the Galiant Beast model). You'll need to do some editing to make this model playable (I believe we recycled one of Vincents several battle models) it'll need a valid battle model file (such as RTAA). Once you have this you have a playable character full of animations of their own you can use. At this point you can probably make the Supernova attack an available limit break.
For the Red Werewolf we actually reused quite a few of Vincents limit break attacks, and you can also tweak the actual animations to better fit your model.
For actual character animations this is a lot more work. To make the Red Werewolf stand up and walk around we used Barret's skeleton and a mixture of his and Cloud's animations (they're pretty similar, other than their feet). From there you can select which animations you need for the various actions this character will make (if they're a member of your team or seen in the field). This process can take awhile though, I believe Wolfman and I spent 2 weeks or more editing and creating brand new animations.
I can offer insight for the animations and adding limit breaks for characters, but actually making a model available as a teammate is outside my knowledge, we had help with that part. Didn't seem difficult, you just have to know how to do it (or it was just made to look easy lol, not to undersell the complexity involved). I think that answered your question, but maybe a bit off topic since your talking about new bosses instead of a new team character.
