Use IEASVCxx to define your installation's own SVCs, which can be numbered from 200 through 255.
During system initialization, the system reads the IEASVCxx members, and places any SVCs you specified in the SVC table.
To dynamically replace or delete SVC table entries use the SVCUPDTE macro. For more information, see z/OS MVS Programming: Authorized Assembler Services Reference SET-WTO.