Hi Prakash,
1. You can either change abndwidth the filters or other components used in your system manually or using script mode for the parameter. If you relate the value of bandwidth to the bit rate using script mode, then it will automatically change in accordance with the bit rate.
2.Sometimes some parameters in the system (such as filters cut-off frequency) are defined as a function of symbol rate (instead of bit rate). Then this will play a role. I don’t know its exact effect otherwise.
Regards