I just unaccepted an old answer and reselected a community wiki answer on an old question of mine:
I appear to have lost 2 rep points for this action. Why is that?
Normally, when you accept an answer, you are given 2 reputation points.
However, that does not apply when you accept an answer you posted yourself, or if the answer is a community wiki answer. The answer you have now accepted, is a community wiki (CW) post.
So when you switched your accepted answer flag to that one, you lost the 2 points for having accepted the other answer, and did not gain them again for accepting the CW answer.
Accepting the old answer gave you +2 points. Unaccepting took them away again.
You don't gain those points for accepting a CW answer, so you didn't get +2 again.