Nevermind. I fixed this by renaming the chapter's .sav to .mod, then editing it with Leto. Editing the module.ifo, then going to the character and changing the player name. Saving the modified module.ifo, then importing it back into the chapter's .mod by changing the name (again) to .hak, using nwhak to import, then finally saving then renaming from .hak back to the original .sav.
Leaving this here in case someone ever has the same problem.
I'm only curious why the module.ifo ended up being nearly twice the size as the original having only edited a name. Weird. Oh well. It works and that's all I care about.