Hello Vishnu,
MRP would generate exception messages for rescheduling in or rescheduling out, and as all other experts here have pointed out your planner or MRP controller should manually analyze these exceptions and manually change the MRP element dates.
In addition to what other experts have added above, may be you would want to have a look at the MRP exception monitor tool which is offered for purchase by SAP consulting solutions, below link might be of interest to you & your company,
Effective Materials Planning with the MRP Monitor
Supply Chain Management - Details on Service Offerings - Logistics Consulting - SCN Wiki
Best Regards,
Ameya Beri