Hello Vijaya
There is no specific CR type for extend but you can create the CR types based on the requirement. I am using CUST2P1 CR type for extend as its nothing but change of customer.
For the extend process, we have disable all the UIBB's except the sales org and general view as we don't want the user to change or update any other data. The extend process is basically localized (based on region) and general view where normally we enter the CR description and other details. While extending the customer to new sales area
Kiran