Can I limit to one subscription at a time?

Hey,

is it possible to limit this plugin so that a user only has access to one subscription at any time?

If not, is there a list of hooks/codex where I can manually code a solution to this?

I'm looking in the database and currently in the

wp_m_membership_relations table, a user can have more than one subscription.

Would it be possible through the use of your hooks/help to program a solution along the lines of "if user id X currently exist in the table, delete that row and insert this new row."

Thanks!