In reply to chintanmehta:
I strongly discourage modification of the UVM base class library yourself—it becomes a maintenance and migration headache later.
Instead I suggest using uvm_config_db#(uvm_object_wrapper)::set() which has the last-write-wins use model you are looking for.
One thing that does not make sense to me is you are calling create() in your base test, and overrides in your extended tests? Then how are you distinguishing between the different instance?