Hello Tze, to change "Common task" you can use authorization object "SM_WC_VIEW", you will find more information on "Security Guide SP8" on http://service.sap.com/instguides -> sap components -> sap solman -> <current release>.
The popup is loaded because on dno_cust04 you have two transaction types available, if you delete SMCR you will not see that popup, and you will work with ZMCR by default when open ITSM.
if you use ZMCR as your own customized transaction type you don't need standard one.
Regards,
Luis