A quick look of all the contracts I have worked on it – only the SPT disallows it. (Some say specifically musical director, dance captain, fight captain and stage manager only can give notes).
So, apparently, the less you are paid, the more protection you get for half-hour.
I have always given notes during half-hour, but not for arty stuff - but, maybe things like a new prop in the show, a lighting instrument that is out, a wheelchair in the house which may effect an entrance . . . etc.
I think the cultural issue is AEA on AEA notes are somehow okay – weather it be a fight captain, dance captain or Stage Manager – as long as it is maintenance and not NEW material (the SPT contract has very specific rules about rehearsal that is for maintenance versus NEW material).
One of the reasons I love doing musicals is that there is so much more support – dance captain, music director, etc, etc . . . and during musicals, often, a dance captain may give notes or even rehearse DURING the show – especially for new split tracks, etc.
I think culturally, we are set up for that. If someone had a problem with these notes after half-hour, I would look at the specifics of the contract and figure o the kosher way to get these notes out.