Storing descriptors
Descriptors that are created during system definition are stored in the IMS.PROCLIB member, DFSDSCMx. Subsequent system definitions of the same stage-1 input deck overwrite the DFSDSCMx member.
Recommendation: To avoid losing
descriptors when member DFSDSCMx is replaced, store descriptors that
you create by using TSO or z/OS® utilities
in IMS.PROCLIB member, DFSDSCTy.
If you need to update descriptors that are created at system definition
in DFSDSCMx, use TSO or a z/OS utility
(such as IEBUPDTE) to make the updates.