Ability import people from one league session to another, especially when a larger number of people

I have a league session with a max of 200 spots. I have over 100 customers in the league that opt in the weeks they want to play. My league session runs 12 weeks. Then i start a new session and want to import players who were active in the previous league from the previous session in before opening available people. Registering for them is time consuming and asking them to register has a risk to losing their commmitment.