how to change the skill "possess"

Well I made it work..I changed the skill possess to a spell casted, in this case fire. It was simply, the only thing to watch is to jump at the right place at the end. I used Storm code as a base. You can change the #$00 to any other magic. You can make possess behave like any command but the code would be different each time.:

Code:

C2/17E5: A9 00           LDA #$00       (fire)
C2/17E7: 85 B6           STA $B6        (Set spell/animation)
C2/17E9: A9 02           LDA #$02       (Magic)
C2/17EB: 85 B5           STA $B5        (Set command)
C2/17ED: 4C 5F 17        JMP $175F      (jump to subroutine C2/175F)
C2/18F0: EA              NOP            (nothing)
C2/18F1: EA              NOP            (nothing)
C2/18F2: EA              NOP            (nothing)

Here's a video showing the change: http://www.youtube.com/watch?v=89B42bQ003Q

I would toy with it if I had a decent hex editor that does not crash my rom, anytime I do hex editing(well most of the time, sometimes I end up coding something by accident) If I had a good hex editor, maybe just maybe i would.

Unless you use a really deficient product, a hex editor doesn't make a ROM crash. Try WindHex or HxD, they are free and work fine. It might also be your coding that make your ROM crash...