Read or write access of a register through ral back door access will reflect instant changes as it doesn’t involve front door driver transactions.
My Doubt here is when is the requirement for Back door ral access in real case scenario.
In reply to Arun_Rajha:
If your design has thousands of registers which need to be programmed, and each register write takes several clock cycles, it could take a long time to configure the DUT. Using back-door register writes can accomplish this in zero simulation time.