Royan, you`re right, but this is all still planning phase. The question was, whether this still applies when you`re airborne.
These rules do not apply when inflight.
Inflight the only rule is: The captain should be convinced a normal safe landing can be made.
If you start replanning in flight, say 4 hours out and picking another alternate due wx, then ofcourse the planning rules apply. (although this is always the focal point of discussion)