Withholding tax related issue , exemption certificate no

Hi All,

i have one query , vendor master , our client has two TDS Exemption certificate , he want to use one withholding tax type , but vendor master , there is no option for two  Exemption certificate no , so he want to use both TDS exemption certificate at the time one withholding tax type , it is possible or not ,pls give details of TDS Exemption certificate , what basis vendor get tds exemption certificate , how many time get this certificate.

Thanks & Regards

Ajay