Yes you can as long as you don’t have limit reached. My cap was 3 yrs then it won’t let me add anymore on it. It’s eventually a 2 yr cap because Microsoft gets greedy. 15$ today and then it raises cost to 17$ or one day 20$. Ea is included in ultimate now so it’s possible to raise costs. Try it out with true 3 months ultimate eventually it caps out. I add 3 months after 4 months pass by. Eventually it won’t honor cards if Microsoft forces us to link a credit card to account as automatic enrollment becomes mandatory.