Can I change the files spellfix.txt and substitutes.tht? This is correct?

You may change them.  You are then responsible for either IGNORING my versions when new CS releases come out, or merging/modifying mine to match your changes.

Thank you. To me this is important

Of course. Hence the design of the LIVEDATA folder, so it can be custom edited.

You can also selectively simply disable from script using one of those files.  You add to $tokens a value to discard a particular file.