Deletion/Expiry of TSM files by adjusting TSM configuration?

[ChrisCorfield]

We have a large TSM system for archiving Content Manager OnDemand files. This system uses an archive Copygroup with "Retention Initiation" (RETINIT) defined as "CREATION", and "Retain Version" (RETVER) set to "NoLimit". We also have archive retention protection set on, for storage hardware compatibility. We now require to delete/expire some files and want to achieve this for example by changing RETINIT to "EVENT". We also attempted reducing RETVER but get the following error:

ANR1620E The new RETVER value (0) is less than the value in the ACTIVE policy (32767) for CREATEDOM CREATEPOL CREATEMG.

In summary we have not found an IBM documented way of doing this. Any thoughts or advice welcome. Thanks.