Might it be in the file/folder name instead of file content?
No files are named that way. I did however figure out that while I was doing a text search for "NPUH-XXXXX" in the decrypted eboot, the eboot file also had a bunch of listings for "NPUHXXXXX", mostly in reference where files are located.
EDIT: Changing the numbers there does nothing to change the game ID when played in PPSSPP. This is also the ONLY file in the entire ISO that contains that string.
I was hoping that there would be a standardized way of changing game IDs for all PSP games, but that doesn't seem to be the case.
I can find tons of information on changing PSX game IDs to work on PSP, but I can't find any information on changing an existing PSP ID to a new ID.
EDIT2: Changing the param.sfo file seems to make the game ID show up differently in ppsspp, but the game still shows up as the old ID when playing online. Changing the eboot and param.sfo makes it unable to connect to the server, which seems maybe more like a problem with the server not recognizing the game. I think that is the issue though