In general, you can’t. Most projects are OK with flipping options and running off of cached results, but others are not. I’ll also note that Find modules usually want everything they make cleared before finding a different installation of the same package though.
It probably should. CMake doesn’t support changing the compiler after the initial configure (where a compiler is successfully found) because it builds all kinds of knowledge up based on that discovered compiler that undoing it all is very unreliable, so it’s just best to start from scratch in that case.