In anticipation of the change to AllowUserKeyCSA(NO), all CVs must be changed to run in key(4).
However, all CVs execute the same startup program RHDCOMVS, so if the new PPT entry for RHDCOMVS is added, it will affect all CVs once it is enabled.
How can this be tested one CV at a time?
Release: All supported releases.
Documentation on bringing IDMS CVs up in the recommended KEY(4) is at Storage Key Considerations for z/OS CSA Subpools.
It is true that CVs will typically execute the same startup program name RHDCOMVS (or alias IDMSDC which some clients use), so that if a z/OS PPT entry is for this program name is added, it will affect all CVs.
However, the PPT entry attributes such as KEY will only be honored if the STEPLIB from which the startup program is loaded is APF authorized. Therefore, to test one CV at a time, add the PPT entry, then ensure that the STEPLIB in the startup JCL for the CV to be tested in the specified KEY has an APF authorized STEPLIB and all other CVs have STEPLIB that is not APF authorized (adding a non-APF loadlib at the bottom of the STEPLIB concatenation will effectively make the STEPLIB not APF).
This way, to test the next CV, simply remove the non-APF loadlib from STEPLIB so it includes only APF-authorized loadlib(s).