Shock Ability

So, this is assembly code, which is kind of a step above direct hex editing. You can save this in a plain text file with a .asm file extension, and then use an assembler (xkas is most common, but I use asar, which uses the same syntax) to patch it onto the ROM. I believe both of those are available on the wiki, under the utilities section?

There's no freespace conflict with the stuff you're editing with FF3usME, thankfully -- all of that data is stored elsewhere in the ROM. This is using some unused space in the C2 codebank, which primarily handles the battle functionality. (C1 handles battle graphics, C3 handles field menu, etc.) There may be a conflict with other patches you've applied, and if so, I can help you find an appropriate place to patch this onto the ROM, but otherwise you can just assemble this onto the ROM and you'll be good to go!

One thing to note: if you're using xkas and your ROM is headered, delete the semi-colon before "header" at the start of the code or it'll patch over the wrong sections of the ROM. If you're using asar, it uses the file extension of the ROM to determine whether or not it's headered -- .sfc for no header, .smc for header.