Me. Rev. Stat. tit. 32, § 18557

Active duty military personnel, or their spouses, must designate a home state where the individual has a current license in good standing. The individual may retain the home state designation during the period the service member is on active duty. Subsequent to designating a home state, the individual may only change the home state through application for licensure in the new state or through the process outlined in section 18556.