There's a mod over at Nexusmods that enables you to substitute the Serah model for Lightning. It's not perfect, but it's pretty good. Pre-rendered cutscenes will still show Lightning and the voice will still be Lightning.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1918636715

There is an optional "Hard Mode" file download. It below the "Main Files" section.

Coming soon... A little more testing required, but I will be uploading a mod that will allow you to customize the hair color of all 6 main characters (not including the pre-rendered cutscenes). Snow, I think, looks better with dark hair.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1883744475

Edit: Uploaded to Nexusmods

I think I might know how to give Ultima a name. I'm not sure if it will change anything else. I hoping to be able to spend some time on this (and some other mods I'm been occasionally been working on) this weekend.

I'm kind of surprised there were so few mods made back when this game was new to the PC. It seems like there is some potential here.

Didn't have a lot of time tonight, but I did find the bit that allows the enemy attacks to show up in the character list. In the Excel wdb spreadsheet in the bt_ability file, it is column BM, byte #3. A value of 1 will allow it to be selected in battle. Unfortunately, all the ones I've tested are like your Eidolon attacks. Lightning might run up, but nothing happens. I'm going to start looking in the damage file, maybe something is there, or perhaps it's more integrated with the animations themselves somehow where we might not be able to change it (the animations are so different for enemies that perhaps the whole attack sequence aborts so nothing happens)

I haven't tested it out, but I think column BV, the 2nd integer is the number of times an attack hits. It has a value of 17 for cold blood, and has values > 0 for other attacks that hit multiple times (a 0 seems to be just a single hit). Aof1 is a 0, not an 11 like I would expect, but that may be due to the fact that the animation hits 11 times, but each hit is singular, while the cold blood animation only hits once, so it has a "multiplier" of 17. Not sure, just a guess. I'm going to try it out tomorrow.

So I did have a little success with an enemy's attack. Based on your info on the eidolans attacks, I picked an enemy that had very similar ability stats, in this case the Pantheron's War Cry m001_ac100. It did show up in game and I was able to select it during combat. Unfortunately, it's a 1/2 ATB bar skill, so it was stacking on top of one another and I didn't really check to see if it did anything. Based on this, I will try to narrow down, what parameter in the ability file is the critical one.

Did you try any abilities that didn't work? That may also help narrow down the problem.

the 65535 is due to the header column (row #1). By default, the values are shown as two unsigned 16 bit integers (ii) where there is no pre-defined definition. In the early part of the documentation, it shows the various acceptable characters you can put in the header to display the data in different formats. The picture is showing the 'w' header (for word - a signed 32 bit integer - yes I know the header in the picture shows an 'l', that's because I took the screen copy when I was using 'l' for long and had to change it but never got around to making more screen copies). The text in the documentation is correct. Once you change the header, click on Fang's picture to redisplay the data with the new formats.

As for the "Role", that's not the problem. A zero in the role makes it available to all roles (I think the Hand Grenade is like that). I also accidentally changed the volley once to a specific role, and it didn't help.

That question is a little tougher... The gameplay tweaks uses standard text file for the included app to read to know how to change the wdb file and there's a batch file that can load the modified wdb back into you game, but I would need to do a write up to really explain how to manually do it. If you're pretty good with batch files and stuff, you can look at some of the gameplay changes I've made in the mod to see how it works.

Let me see what I can come up with over the next couple of days to simplify and document the process.

If you download a 3rd mod - "Gameplay Tweaks and Hard Mode", there is a batch file in there "FF13wdbSetup.bat" that will automatically find your Steam FF13 directory and extract all the .wdb files out of it. If you just run that one batch file, it won't make any changes to your game other than extracting the files.
Make sure you extract this mod into any directory other than where your steam files are. Somewhere in your documents directory will work fine.

Odd. There are two mods, the crystarium mod can only open the crystarium files. The other mod is called "FF XIII Modding Resource". This one has the excel file "FFXIII wdb.xlsm" that should be able to open any .wdb file. (you need macros enabled and must have the desktop version of Office)