For the first time ever, Tricare will host an open enrollment period next month for military families and retirees who want to change their coverage plans. Currently, changing between Tricare Prime and Tricare Select, previously known as Tricare Standard, is easy and typically not time sensitive for active-duty families and retirees. Starting Jan. 1, however, the ability to switch back and forth at will is going away. Here's what you need to know.