The z/OS CSA parameter ALLOWUSERKEYCSA gives you the the ability to specify NO to stop allocation of user key CSA. Does XCOM for z/OS has any issues with the setting ALLOWUSERKEYCSA(NO) in member DIAGxx of SYS1.PARMLIB?
The ALLOWUSERKEYCSA parameter does not affect XCOM for z/OS, since XCOM does not allocate any storage in the CSA.