Swapping directional tires to opposite side

[j.fro]

Removing the tire and reinstalling it can cause the bead to fail. Every time you remove and reinstall, you have to stretch the bead to get the tire on the rim. Tires aren't designed for the bead to be stretched over and over- they're made to stretch just once during initial installation. Given that, I've done exactly what you are thinking of with my own directional all season tires and gotten a few more miles from them, and never had a failure (one "switch" only!).
I would NEVER do this with a track tire - way too much stress and risk!