Hi Faith,
The CTT assignment can be changed, if the child's needs change. When my son was in CTT, I had an IEP review meeting with his teachers each spring and we discussed what he would need for the next year. After several years in CTT, my son is now in gen ed and doing well. So the short answer is yes, if there comes a time when the support is no longer needed, the class assignment can be changed.
Just want to add: I loved CTT and thought it was a great program.