Um, I think that is TOTALLY splitting hairs. How do you give a "maintenance" note without giving an "acting" note.
If you are charged with with maintaining the show artistically, then you are going to have to give "acting" notes. What happens when you have to put in understudies? or replacements? How do you engage in a conversation when an actor begins to stray, but they defend it with shooting back justification based upon motivation and emotion. (Actor A says Actor B is changing their performance, Actor B claims it is the right motivation based on something Actor A is doing . . . ) If you can enage an artist in an artistic conversation you are going to get a lot further then just saying "stop doing that" or "just do it the way you used to do it."
100's of little things change in the show, especially in a long run of a show - you are never going to keep the show EXACTLY the way a show played opening night, and to be honest, most directors would want a show to grow. You need to be able to give "acting" notes, you need to be able to engage an actor in an "artistic" conversation about their work. It's sort of part of the standard definition of our job - now as a student, or being a SM on a short run, or if there is someone else charged with the artistic quality of the production - then it's not your job, but most theatre's would expect you to maintain the show artistically as well as technically.
My job isn't to create a photo copy of the show on opening, but allow the normal growth of a performance to happen. Think of it as gardening and tending to a topiary. If the show is in the shape of horse when it opens, I need to make sure it doesn't end up as a unicorn, or a bear or a moose. But letting the show grow, and fill out, and grow into those bare patches that were there.
It's important - from the very beginning of table work - for a stage manager to start crawling into the director's head, taking notes, and be have all the documentation to back up what the director had in mind - but ultimately, a production becomes it's own entity. For example, on my current production, once the (positive) reviews hit, although the performance didn't change, immediately changes happened in the audience's reaction - the laughed a lot more, they responded a lot more - the actors had to learn how to hold for laughter, navigate audience reaction, hold blocking back a bit - all things that effected the acting. I couldn't tell them to just do the show as they did opening night. (On a related note, I have had to adjust cue calling as the show adjusted to the audience.)
When an understudy goes on, I always make it clear that me and the understudy are going to meet after the show to go over notes - help them with their acting - help them with their emotions and motivation for scenes.
Also, there is a lot of just reminding them of their motivation and emotions in keeping the show true to the director's vision in the long run. 6, 8, 12, 24 weeks into the run - you will find yourself having these "Artistic" conversations.
This is one of the major reasons every stage manager should have some sort of directing background (along with design) - we are just secretaries, schedulers, disciplinarians and cue callers - we are a part of the artistic team - as well as the technical team.
I know you are trying to draw a line in the sand, and say this type of note is okay, and this type of note if forbidden. But in reality, at least with my style of stage management, and at the level I work as a stage manager, there are A LOT of "acting" notes given - and I am the second in command behind an assistant director who also is charged with the front line of maintaining the show.
I think as a younger stage manager, it might be good to be able to draw those lines in the sand, but as you continue down this path . . . you will find yourself being able to comfortably take on more and more responsibility.