Unfortunately, there would be no way for a client to do this against only "selective" job's MSGCLASS output. This is because of the way that MSGCLASS data actually gets archived. The process used to archive MSGCLASS is different than archival process used for REPORTS in that, we don't use a "VRDMU110 - Report Base Definition" database specification to determine what media MSGCLASS data should be archive to.
CA Dispatch only uses the VRDMU110 screen definitions for archiving of REPORT data. Not MSGCLASS data.
The report=MSGCLASS ; jobname=(BLANK) definition that you see on the VRDMI100 screen display is NOT used for archiving MSGCLASS data either.
We do provide Special Feature FEAT022 which allows you to change the "DEFAULT" archive media. However, if this particular Special Feature is applied, it would be applicable to "ALL" of the MSGCLASS data archived after it is applied. You would still not be able to be "selective" in terms of which job's MSGCLASS outputs goes to which archive media.