^I'm not a SC mod, but I don't think that's possible. Besides taking a lot of time, it's not an easy job to follow every time a model changes agencies...I think if I eventually notice a model I follow switches agencies, I can easily add that information to the first post of her/his thread, but I don't believe we can guaranteed that for all models' threads. My two cents.
There's a
Models Switching Agencies thread, hope it will be helpful for you.