Changing a Management Class for a TDP Exchange Node

We use MC with VERE + VERD=Nolimit and RETE + RETO=30 days, weekly full backups, daily incrementals. We want to keep already backed up files longer than 30 days. What happens if we replace this MC for our TSM node with an MC with RETE + RETO=60 days. I suppose that changing the MC in the client opt files would only keep the full backups for 60 days by rebinding them while the existing incremental backups still expire after 30 days (no rebinding because they are unique). Am I right ? If so, is there any way to keep already existing backups (both full an incrementals) longer than 30 days ?
Thanks a lot !
zgzg