Hi Ben,
I re-read your question and now I'm not sure about your question. Do you mean the scenario which I explained above, i.e., you let SYSTEM create USER_A and you want SYSTEM can see the schema USER_A under his "Catalog" folder or you want to login with the new user USER_A?
If you want to login with the new user, you can right click the current system and choose "Add System with Different User", then you input the username and password to login. You may required to change the password.
Best regards,
Wenjun