Standard field mandatory validation

Hello to All

Currently we are using SAP SRM 7.0.

We have to remove  mandatory(State = Required) for one of the input filed, for this I have written the code in pre-exit, but it has been remove only Red mark * infront of Input field, after that, when we trying to save other data, still it is asking me enter the required value.

Can any one suggest on this issue.

Thanks & Regards,

Kamal