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Maybe a "set to default" button, even then you'll never account for every mistake and experiment a user can, and will attemp.

That should help. I'll also load the default values in case of a vanilla ROM based on the MD5 or SHA-225 / SHA-512 value. I could also save these and other settings based on the ROM hash.

You really can't blame anyone that once said it couldn't be done. Course, some people have used it and done things so the concept is sound. If you can make any improvements on your's, it is bound to be useful to someone.   

I'd blame anyone telling it can't be done, easily done in a proper way probably not but far from impossible. I'm still thinking about it and it could be a mix of inputting the hex commands directly for the veterans or choosing from a menu for newbies with a dynamic disassembly for what you input serving as a guide. Once you save your portion of code, it either push and reorganize following code or overwrite based on the option checked. In case it pushes the code, whole disassembly is reloaded, same thing if you just remove bits of event code.

are you planning on having an option for changing the "starting spell value" for the commands that use spell rranges?

Yes, I've found all the data regarding the Magitek menu (Terra specific and default), starting Rages, Lores, natural magic tables and Blitz / SwTech learned at level up. However most of these cannot be expanded (except rages that allow technically 32) without ARM changes that I have not identified.