Rishi,
Thank you for your reply. My question was when a std. role is included in composite role (and included in transport, otherwise composite role won't work) and that transport is imported to upgraded system, will it overwrite the existing Std. sap role...
The answer appears to be yes... I checked the same role in a different system and when I compared the authorization objects between upgraded system with overwritten roles and default role, it did not have the same authorization objects.. I am surprised that SAP makes it a mandatory that std. roles which are included in the composite role must be included in the transport request.