Question: Changing a Battle Command to a single spell

How do I change the command ID to #02 by storing it in $b5? I'm not familiar with this, and it seems to be the thing getting in the way of my success. Is it possible to do this with just a Hex Editor? So far I've only been hex editing and not doing any assembly.

Also, on a slightly-related note, could a command be programmed to have the same effect as a Smoke Bomb? My thief could have the "Flee" command if it were possible.

What you're looking for is in the code block at the end of my post.  We're going to take this code and apply it over Possess.

As for making GP Rain into another 'cast spell' command like health, you're going to have to apply hex like the following with a hex editor like HxD.

Code:

Spell [Was GP Rain]
C2/1907: A9 59        LDA #$59       (Spell d89 [h59], Empowerer)
c2/1909: 85 B6        STA $B6        (Set spell/animation)
c2/190b: A9 02        LDA #$02
c2/190d: 85 B6        STA $B6        (Set command to Magic)
c2/190f: A9 05        LDA #$05
c2/1911: 4C 65 17     JMP $1765      (Go to the end of the Slot command)
c2/1914: EA EA        NOP

This changes the spell being called by the command, tells the game to treat the command like magic, and then executes one hit.  If you want the command to skip MP depletion, you can change the LDA #$02 to LDA #$0F, Slot.  If you want it to keep a custom animation (default, throwing coins), then change c2/190b and c2/190d to 80 02 EA EA.

NOTE: This will take its targeting from the command, not the spell you select.  So, if you set the command to target all in FF3USME it will, even though Empowerer is single-target.  Getting the command to target based on spell targeting is a little more complicated; it draws some design from actions like Rage.  I've got notes on it, but not on hand at the moment... we can discuss it later if the need arises.

Try taking these hex values:

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).