nevermind...
here's how - in the scenes view (personalize, scenes) press-and-hold on a given theme and you're able to rename it
doesn't look like you can "add" a new scene - you just end up renaming the current ones :/
so if you want to keep the stock scenes and modify them to your liking, and then give your new creations a unique name... i think you're out of luck
but i'm not sure - still looking into this...