Thanks for the reply. 
Yep, I’m in the same boat here. It looks like reloading this saved flight some time tomorrow might be the only way to know if Live Weather now updates after loading saved flights (strange that MS would leave such a big improvement off their notes, if so?).
What doesn’t help is that the toolbar is still disabled/limited after loading, so it’s something that’s gonna have to be judged with the naked eye or using the cockpit weather systems.
If anyone else has already tested this, please feel free to chime in.