I'd say it depends on the MPP. If the MPP was a 401(a) plan, I cannot see how money could be transferred from a 401(a) plan to a 403(B) plan. (You can click
here to see an article which describes the current law restrictions on transfers between 401(a) and 403(B) plans.) However, I have seen an occasional MPP which is structured as a 403(B) plan, in which case converting it into a different type of 403(B) plan should not be a problem.