Unless the developer decided to add something to the characters, I don't think that I have to reinstall anything, unless I'm wrong. If you're wondering, I think I downloaded this mod: http://community.playstarbound.com/threads/mod-portraits-like-anime-style.107707/
AFAIK art mods should be good, unless the update specifically altered the files that the artist edited. Mods using various APIs may break until the API/mod are fixed.
Yeah, like Kamirose said. If only the Grafik on the file is changed, nothing will happen at all. It could only get replaced from a Update when it give a new file for that cuz its a new grafic or similar.
I had to reinstall all of my portrait, animal, character, and loose sprite mods after this last update on Thursday I think it was. So, maybe? I really don't know what the update targeted so I have no idea why I had to reinstall everything.
The update removed a mod in the cursors file, but that's because the cursors sheet changed to add the zoom buttons.