Yes, it pops the stack value into the CS register. But it doesn't update the PC as well - it'll continue to point to the offset (in the old CS) of the instruction after the "POP CS". So whatever code is in the new CS, it has to be "compatible" with the code in the old CS, in terms of the instructions starting in the right place. However, it's even more complicated than that because the prefetch queue is not flushed, so the exact address where it switches over will be unpredictable. For certain very specific scenarios it could potentially be useful to speed up conditional execution by eliminating those prefetch queue flushes, though.
