User Exit/Enhancement to populate the characteristic value during runtime in FB50

Hi

I have a requirement where in FB50 when I enter the GL Account , Tax Code, Tax Jurisdiction code and Assignment and press enter  I need to default some of the characteristics value (which comes in the popup when you click on the Profit. Sgment ).

Please let me know if any enhance or exit is there to achieve this.

FB50 screen.

When I enter the GL account and click on Profit Segment button below popup will come . I want to default Rebate field with some value.

Thanks,

Sumit