Dynamically update annual recurring billing date auth.net

Hi ALL
I am using s2 members pro to set annual subscriptions for sending digital cards. when signing up we give 60 days free but if a members sends a certain amount of cards then we give them an extra month - I can update this in the EOT meta but will need to update the auth.net recurring payment date by an extra month, is this possible and would it be similar to https://www.s2member.com/forums/topic/modifying-monthly-recurring-amt-w-authorize/ although there is no date field?

Many Thanks
Wayne

Looks like it’s possible to change the recurring sum by Auth.net, so you can set “this member” to be charged for 11 months, instead for full year, next time he needs to upgrade. But also must set back the annual sum after the member (actually, Auth.net) send money, so next year to be charged without reduce… Well, I am curious to create automated script to do that, if you want.

Thanks for the reply.
Charging for 11 month makes sense and a potential option, but will be difficult in our pricing structure at it is an annual membership of £10.00. Is it possible to change the scheduled date from s2 to aut.net dynamically, will it require user agreement as that payment date will change?

Thanks

Wayne