The note attached to said rule states "A pitcher may change to another position only once during the same inning; e.g. the pitcher will not be allowed to assume a position other than pitcher more than once in the same inning."

Does this mean a pitcher may move to another position and return to pitching all in the same inning?

Yes.

It's happened a few time is MLB.

I saw it happen in an old time baseball movie. I can't remember what it was though. A new pitcher was subbed in for the third basemen. Then the new pitcher switched to pitching and the old pitcher to third base. The after one batter they switched back.