I don't think there's a built-in downgrade feature from Professional to Community Edition. As it was noted here in this question, DNN professional and DNN Community Edition share the same codebase. In other words, DNN Pro is DNN CE with some extra built-in extensions such as document manager, impersonate user, different caching, etc. That means 99.9% of modules and skins will run fine in either edition.
Option 1: Seems tedious but would surely work.
Option 2: I would make a backup copy of the site on a development machine and try to do it there before attempting it on the production server. Please post the results for this if you try it.
Good luck.