Sorry for the lack of replies lately. I've been busy with another project (and haven't had much spare time anyway, TBH..).
any chance someone can just upload rebirth somewhere?
As others have said, this would violate the boards' policy on piracy. You can try applying the patch on a later version of the game though. It could work just fine. If not, absolute worst case, you'll only have wasted a few moments trying. Really, the game just needs a few .dxa files. If the only changes between your version and 2.04 are changes to the exe and not the dxa files, everything will be fine.
to make it more interesting, you should take some of the mediocre characters like rumia, remilia, and rinnosuke and just completely rework them with new skill sets as well.
I'm sure you'll be quite pleased with the changes made in LoTR (if you haven't gotten it to work yet).

Edit: My bad, I think I misunderstood what you were saying. It would be difficult to do anything about the characters that are no longer in LoTR but those that still are could certainly be modified. Feel free to post your ideas; right now, most changes being made involve the remaining original LoT characters so, yeah... it's the right time for these sort of suggestions.

(boss ai...)
Well, others have already answered this, but for what it's worth,
here is the AI it normally uses. As you can see, it skips over invalid cases in its regular behavior without using up a turn. You're VERY, VERY likely to see Flowing Hellfire every single turn if only the 4th slot contains a character (>90% odds of skipping all 3 single-target attacks) because of the low odds of that slot being chosen.
I've consolidated changes to the unmodified characters into a list based on what was discussed in earlier posts (mainly by Reiska; don't worry, I didn't just skip over that wall of text

) and will be posting it in a few days to see if anyone has anything to say about the changes before I implement them. Probably this weekend.