Modify PHPBB usergroup / Paypal Payment Intigration

I have a PHPBB forum. I have created a user group titled “Kingpin Members” As of now the “kingpin member” usergroup is set to “open” meaning anyone can be a member of that group. I would like to modify the Kingpin member group to be “free access for a limited time / trial” then member must activate a paypal subscription to continue to be in the “kingpin member” usergroup 1.) Free trial available with. No credit card or paypal subscription required. Member joins group and gets instant access. (provide me with instructions on where in the code I go to edit how many days the free trial is) 2.) Once free trial expires members usergroup changes to “Trial Expired” usergroup. At this point to get back into the “kingpin member” usergroup they must activate a monthly subscription via paypal 3.) Each month if subscription is not paid then the go back to “expired” usergroup. 4.) Member can only take advantage of free trial 1 time. There will be some times where I decide to give free access to a member. I will need instructions on how to edit that users "payment due date" in the database to a date FAR in the [login to view URL] way that member never has to have an active subscription