I don't think the game currently has this (but I can see how it would be a great new feature--to try different combinations to see what works best)
But there might be a workaround. You still have that game (number) saved, right? All you have to do is reload that game, write down each card in the kingdom, and then create a new game with those cards. I am hoping that this will "reset" things so that you have a new game.
(If Dominion, instead, looks at your kingdom and says to itself, "Hey, that's exactly game 1234567 at Tokyo!", and loads that game, then the workaround will not work, I presume.)
Please post back here and let us know the results. There definitely have been games where I say to myself, "I wonder--would I have won if I had gone traditional instead of Duke/Dutchy?" or other strategic decisions like that.