How to Make Your Own Version

First, use the Library Manager and give it a release zip, this will install Watchy_GSR as a library, go into the Watchy_GSR library and move the GSR.ino out of it and place it into where your project is. Rename it to something like MyGSR.ino and edit it, you can do all of your overrides in that. That ino file now becomes your main compile file.

If you're updating Watchy_GSR, be sure to remove the GSR.ino from it after the Library Manager has imported everything.