I have question about paid and free + ad-based apps/games in wp7 marketplace, can I publish my app as paid version initially and later(after a month or so) can i publish the same app/game as free + ad based version? Is there any such rule/policy in wp7 marketplace. I could not find proper answer on the net not lucky enough. And i hope this is not off topic question. - Thanks
Yes, you can do this. In the settings for your app you get to set the price and "Free" is one of the options.
Some things to consider before doing it: