Eric
There is nothing to stop you changing CAMOs each year. In fact that would be the situation if you went into the 'uncontrolled environment'. But the problem that would result from this is that each ARC would effectively be a Star Annual.
The CAA have already stated that they would prefer us to have a long-term arrangement with our MOs and so by staying the in the 'controlled environment' we have the current situation of Star-annual-annual-Star annuals, which should cost a lot less.