I am not a fan of the flavor of the wilton fondant, So I have been makin the MMF, can I add butter flavor to it to change the marshmallow taste?

You can flavor it with ANYTHING! There are so many flavoring oils to choose from!

flavoring oil? can you use extracts? or is that the same thing?

I always just use any old flavoring that I want to. I add it instead of water when melting the marshmallows, that way they don't get to sticky.

You can use a couple of drops of Lorann oils too....kids love it when I use the cotton candy flavor for it! You can make it any flavor you want - just as the PP's said.