The add-on I'm looking at just mentions mostly suspension and deletion, but to change their primary group is something I haven't seen an add-on accomplish yet. If we had the add-on automatically add the user to a secondary group, they will still be able to view and do whatever on the forum because the primary group will always trump the secondary in terms of permission. I think I may look into developing a "Deactivate Account" add-on instead that simply switches the user's primary group into an actually semi-banned state where they would only be able to see a section we would specify in the add-on settings. Fortunately for us, XF makes it so you can't remove any of the "deleted" user's content, especially if you preserved their username. and didn't opt for the username change that can come with the "deletion".