Giving Gau's Magic to Umaro

You'll need to remove some checks for Gogo AND above IDs such as this one (search "gogo" or "Umaro" in bank $C2). The following is done after battle:

Code:

C2/5E59: B9 D8 3E     LDA $3ED8,Y (Which character it is)
C2/5E5C: C9 0C        CMP #$0C
C2/5E5E: B0 13        BCS $5E73   (Branch if Gogo or Umaro)
C2/5E60: 20 83 62     JSR $6283   (Stores address for spells known by character in $F4)

You'll need to modify the following code; if actor ID == $0D, do $0B * 54 instead of $0D * 54. I'm not sure if the actor ID in X is reused later so you might have to save it and restore the real actor ID after this function.

Code:

Stores address for spells known by character in $F4

C2/6283: 08           PHP
C2/6284: EB           XBA
C2/6285: A9 36        LDA #$36      ; # of spells per character
C2/6287: 20 81 47     JSR $4781     ; Character ID (in X) * 54
C2/628A: C2 21        REP #$21
C2/628C: 69 6E 1A     ADC #$1A6E    ; multiplication result + Base offset (Terra's fire spell address)
C2/628F: 85 F4        STA $F4       ; store to use later
C2/6291: 28           PLP
C2/6292: 60           RTS

There will be other things to modify, as an example for magic list loading during battle likely. This is also in bank $C2. You'll need to use the same concept as swapping $0D for $0B for the time you need.

Edit: Similar code at C2/56CC.