Waitlist policy is configured on season level, it can be customized in each session but the change made on a specific session will automatically apply to all the rest of sessions in the season. 

After the season is activated, when you add a new session with default waitlist policy configured, all customized waitlist policies that have been created for the rest of sessions will be changed back to the default one automatically. 

Note: For how to create a waitlist policy, please click visit Creating a Waitlist Policy