What a "meta" question is is  going to be a regular point of confusion for users, and questions *will* get asked under the wrong post type. Being able to fix this with a simple status flag change would be much less messy and disruptive than requiring deletion an reposting.
Top Answer
Let's allow changing the type as long as the post has neither votes, nor answers.

After that, it requires a mod (or deletion + reposting).

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