Possible to have duplicate fully qualified schema names with separate data in DB2 for z/OS?
If the application is hard-coded with the qualifier, then it can only use that qualifier and SCHEMA.table-name is unique.

The best approach is rewrite the application to use unqualified table names.  If you do end up considering creating additional subsystems, you might consider zD&amp;T.  This is z/OS running on Linux on x86 for dev/test environments.  https://developer.ibm.com/mainframe/products/z-systems-development-test-environment/