Well, like I said, you can use KotOR PC Saves, I import mine from my Steam copy successfully, also edited it using KSE. Just make a save on switch then overwrite it using JKSV then restore it.
If you have KotOR 1 on Steam, you can import the save from it, but strangely not vice-versa. You can make/use the save from PC, edit it if you'd like, then import using JKSV.
Huh, on my end I can do it with just the .d2s file alone. Weird. Although I only edit the current char stash to add some rune and charms. Don't want to go overboard with it haha.
Steps? Pretty straightforward actually,
1. Use JKSV to backup the save
2. FTP copy to PC
3. Edit the save
4. FTP copy it back to Switch overwriting it, then restore on JKSV
5. Profit?
Dunno why it didn't work for you.