Question: Changing a Battle Command to a single spell

Try taking these hex values:
Code:

Code:

A9 59 85 B6 A9 02 85 B6 A9 05 4C 65 17 EA EA EA EA

and applying them with a hex editor to address "C2/17E5"

That should make the Possess command cast Empowerer instead, because Empowerer is spell #$59.  Hopefully that works... if it doesn't we'll have to take a more thorough look at the command code (what I wrote for your post was spur-of-the-moment, something I did not test).

That was the code I tried previously and couldn't get to work. I used a fresh FF3 v1.0 rom and it does appear to be doing *something*, but whatever that thing is seems to have a 100% miss rate. I tried changing the spell index to various different spells (Flare, Demi, Haste, Rasp, and Vanish) in the hopes that it was simply "Empowerer" that was giving us trouble, but all of the spell indexes I tried appear to have the same result. 100% miss rate. Next, I tried adding this code in place of the "Sketch" command, in the hopes that maybe the "Possess" command was giving us trouble, but it returned the same results.