Command Change Custom Event

Hey, everyone. Please forgive this bit of thread necromancy.

I'm about ready to release an all-new version of the General Leo hack. I'm a lot more experienced now so I was able to do a lot more and do things more cleanly and bug-free.

There's one last thing I want to implement, though. It looks like the answer is in this thread but I'm having trouble tracking with it.

The idea is that there will be a one-time option to give X-Magic to Terra, Celes, Strago, or Relm. No more Gem Box relic. X-Magic would then permanently replace Magic in the chosen character's command list.

The two-variable option created by GrayShadows seems to be just what I need, but I don't understand how to implement it. Is this just ASM? Does this involve manipulating RAM? I'm not familiar with the notation used.

I'm hoping someone can give me a For Dummies version of this. Thank you!