One of the big problems my site staff has had with tags is the overwhelming number of similar or duplicate tags, due to the write-in ability.
I'm about to add new custom taxonomies to my site for them to use, but I'd like to avoid the problem we had with tags. I'm curious to know if I can turn off write-ins, so they can only be added manually through that taxonomy's part of the admin area. It's non-hierarchical, so they can still type in and the system will auto-complete and search for tags they might be looking for, which is great. I just don't want them to be able to create new tags from the post screen.
Is this possible? I was looking at the Taxonomies and register_taxonomy() pages in the Codex, and thought maybe the "rewrite" function might be what I'm looking for, but I don't think it is now.