Not really, First you should Edit/modify a copy of an original skin. Save it with other name. Edit that new one. Once you're done and satisfied with your work for that part. You can save it and make another version of that and edit that second version one. And so on and so fort. That should save you from start from scratch. But, yes, sadly, there is no undo button in Skinstudios.
Thank you,
Basj,
Stardock Community Assistant