C1/7BA3 in the disassembly is the line for Def in Short Mode and C1/7C20 for Def in Window Mode, telling that to jump to the Item Command will make it open in place of Def, HOWEVER, when I tried it, while it did not crash it was acting the same as when I had 02 at C1/7CAC (items doing oddball attacks instead of their own).
*EDIT* Nevermind that last part, I'm an idiot I never changed C1/7CAC to "01" on the rom I was playing with at work. SO in short, you should be able to follow original instructions regarding C1/7CAC and just change the jumps at C1/7BA3 and /7C20 to repoint Def instead of Row.
Whole thing still needs testing to make sure changing A9FF to A901 doesnt break anything though.
Thinking about it though, I like your idea of replacing Def better.
*EDIT* Nevermind that last part, I'm an idiot I never changed C1/7CAC to "01" on the rom I was playing with at work. SO in short, you should be able to follow original instructions regarding C1/7CAC and just change the jumps at C1/7BA3 and /7C20 to repoint Def instead of Row.
Whole thing still needs testing to make sure changing A9FF to A901 doesnt break anything though.
Thinking about it though, I like your idea of replacing Def better.
The only true wisdom is knowing you know nothing.