As with everyone else, I’ve written before about the merits of using WordPress’ child themes feature rather than hacking the master theme. I’ve recently discovered that not everyone does this, even in cases where the developer claims to be a WordPress expert.
So, if you’re going to do things the wrong way, I have a piece of advice for you: Keep a backup of the original theme that you’re butchering.
At some point, you may decide to get with the program and switch to the parent/child theme arrangement you should have been using all along. When that happens, you’re going to need a copy of the original, as-shipped copy of the theme you mangled, so that you’ll be able to tell what goes into the child theme and what doesn’t.
You may be able to do this anyway, given enough time and effort, but with the original theme code at your disposal, the task is much, much easier.