Top Tip : Reaper also has a Menu entry, just under 'Save project as...'... 'Save new version of project'. This saves the project with an incremented name ('1', then '2', then'3' etc; you get the idea...). Every time that I'm about to make a major change to my stuff, I invoke this, and carry on. Some of my projects have a dozen incremental versions; if I make a mistake (don't laugh; it could happen..!), I can call up any previous version and carry on from there. As can be imagined, I save any adjustments I make very frequently, too.
At project's end, it's simple to delete all the previous stages (I don't; I prefer to keep 'em. Not as nostalgia, but sometimes as a stepping off' point for other projects, but going in a different direction. Yes, I'm daft, no need to rub it in..!).
Hope this helps.