Depends on how popular your module is :)

Instead of changing the API, I think it's much better/easier to rename your API and start fresh, so you don't have to worry about deprecation warnings or early adopters whining about the changes.

All you do is release a final version (unless you want to maintain both APIs) of the old API with a note in the documentation saying something like You should use API2 as API is no longer being maintained (if you wish to take over maintenance ...)