I fear I have been using it to mean a fundamental change in the state of things. I had heard of its origins in Ariel's transmogrification, but had conjured up my own folk etymology to fit with my use of it.

I've always thought of it as a change of seas. That is, the difference in sailing, say, the Caribbean versus the North Atlantic - different worlds, different conditions, different responses required. It somehow became linked in my mind to an image from soccer, when one calls out "switch fields" in calling for a pass from the other side of the field - which requires the defense to shift position to meet a threat coming now from a different direction.

That's my story and I'm sticking to it. Except, of course, to now use the phrase sparingly, and correctly.