There isn't a concept of saving patches as you typically find in synths / workstations unfortunately, it is more like your edits are part of the song / pattern.
I don't remember if there is a way to selectively copy/paste specific data from one song to another and couldn't find this functionality mentioned in the manual. The only way I know how to do it, is to copy the song to a new song slot and then clear the note data. It would be nice if there were a more straightforward way to do it, hopefully there is and I just missed it.
Personally, I prefer to do deeper voice editing from a computer via XG Works, since many more parameters are accessible. This also makes it easy to save the edits as a midi file for transfer to a new song/project. That could be a path to backing up voice edits you made on-device, if you are inclined to explore this option— dump the songs as midi and load the file into a sysex tool or xg works etc, and grab the data from the file for future use.