Every item I've tried has worked thus far.
I did the OP's swap of the sword hilt... for the Demon Hammer. Without pasting entire strings, I changed the digits on the category 40 stuff. I changed the digits on firebomb to soul arrow, result = 6 copies of soul arrow. I changed an undead soul to moonlight butterfly soul. That was with me just changing those 3-4 characters. The possibilities on weapon modding are intriguing, but I didn't know quite enough detail to tinker with that. I'm going to try speculatively adding things from where I imagine the sequence goes.
The bad news, much like my previously edited save, this one also became unloadable (not corrupt). The previous one's data file was completely missing (not even sure how or why that would happen). There's a "phantom save" there now (it shows the the portrait of the character who's save isn't even in the file anymore). I was thinking since this one was also not loading (not corrupt), that it also vanished, got deleted, or whatever's happening to these saves.
The first character (of the three), which was also edited.... still loaded. So, I decided to delete the save from the drive and start from scratch, see if it's more stable. I'll plug in some random values as soon as can accumulate some junk to "alter".