Hi @RobertGibson,
I'll first try to answer your questions to the best of my knowledge.
#1 - You are correct about the name change option, there is one switch that allows users to edit their name info (both display name and regular/legal name). You could potentially put some custom css/javascript in place to try to disable editing of the regular/legal name, though that starts adding a lot of complexity. We don't really have a way of knowing whether Banner will overwrite changes made in the Canvas UI. It's an option that's part of the SIS import process in Canvas, so it just depends on how your Banner to Canvas integration is coded. You'd probably need to set up a few fake users in Banner, then experiment with changing their info in Canvas to see if those changes remain after a few days or if they revert back to what's in Banner.
#2 - That is correct. Display name is not used everywhere in Canvas.
#3 - That is correct. Name and pronouns are part of a user's information in Canvas, so any changes made would be global and affect all of the user's courses.
#4 - Similar to #3, the changes are all to the user's account, not specific past/present/future enrollments. So as long as your Banner to Canvas integration does not overwrite name changes as discussed in #1, the change would be for future courses too.
#5- This is the same as #1. You'd need to do some testing to see how your specific Banner to Canvas process works. There are numerous different ways things could have been coded, so really anything is possible here.
One last comment somewhat on the tech side of things, but getting into policy/procedure a bit... If you allow students to edit their name in Canvas, you'll need to be prepared for a couple things. First, your teachers are going to need to depend on looking at something like a user's login name or email to identify them, especially for purposes of final grade entry in Banner. It's very possible that John Doe could change their name in Canvas to Bruce Wayne, and when your teachers go to do final grade entry in Banner, they will not find a Bruce Wayne at all. Second, users may start to enter inappropriate things for their name. I think that may be slightly more of a concern in K12 than Higher-ed, but it has happened to us a few times in Banner. You can't restrict what students can enter, so you'll probably want to have some kind of process developed for people to report inappropriate names and know ahead of time what someone might do about it (revert the name back to a student's legal name, email them to do it themselves, etc).
I do want to echo the comments made by @paul_fynn while I'm here. I guess I alluded to this in my original post without actually saying it, but I feel like your school/institution should definitely develop some policies and procedures around this. It's definitely not easy work, as there are some very personal and sensitive issues around all of this for users (both students and instructors/staff). The users who want to change name info are honestly probably going to be unhappy with just being able to change name info in Canvas, even though Ido understand it may be easier to enable that option than doing anything in Banner. As Paul mentioned, this is an ever-evolving area and I think we're all learning and trying to do the best we can, so maybe this really is the only thing you can offer your students right now.
The last thing I will say is that we do run a very un-customized/vanilla version of Banner here, as we don't have a ton of staff resources we can devote to developing and maintaining customizations. Enabling preferred name and pronouns in Banner was relatively easy for our IT team as far as I know. The harder work is actually getting other systems to use those names once they are enabled in Banner. It took us a couple years (at least) to track down everything that was using name info from Banner and ensuring it was looking at the preferred name when possible (some things must still use legal name). This is probably what your IT team is referring to, but if it's becoming an issue for your users, it's something that may be worth prioritizing at some point in the near future.
I hope this info helps without sounding too preachy or anything!
-Chris