Edit - back in Nuendo

I have been able to use the Edit button in WaveLab so the song opens Nuendo again for tweaking.
Question 1, is there an easy way to return to Nuendo, instead of manually saving it then going back to WaveLab and replacing it?
Question 2, sometimes (I am in an Audio montage) I cannot use the Edit button because it is greyed out. Is there a reason for this?

Thank you
(newbie)