Okay, I thought I'd have an easy time but it's not quite as easy. I thought I could just stick my own routine in there and be done with it, but it crashed the game. A trace log left me with something missing, and I had to step through the code line by line before I realised what was happening.
The game decides to do a JSR and then PULL THE RETURN LOCATION from the stack and put it in RAM to use as a reference for the pointer table that exists there. I can't stand it when games mess with the stack!
Anyway, these difficulties are why I enjoy ROM hacking, and with a bit more work I'm sure I'll figure something out.
EDIT: I think it's done!
Apply this patch to a ROM that's been patched with the English patch you gave me:http://s346165667.websitehome.co.uk/psyktrans/db3-items.ips
If there's any problem, let me know.