Hi Pedro,
Mainly the screen which appears for PA20 is display only and PA30 with maintenance access this is because the functionalities are hard coded in ABAP program. To answer your question, PA20 won't give you possibility to maintain though you have access maintained as AUTHC = W due the standard SAP code, whereas in PA30 you will get access to maintain and then it checks for AUTHC = W/R in later stage.
Hope this answers your question.
Thanks,
Shiv