Can we automatically change list membership based on a given timeframe

We have a list specific to customers that sign up online vs. in-store. They get an onboarding series for about 33 days before getting added to the main mailing list. I end up going in about once a week and manually updating which lists our contacts are part of.

I'm wondering if there's a way to put a trigger or something at the end of an automated series that will add a contact to our main list and remove them from the onboarding list that contains the automated series.