Adding condition type in VF01.

Hi,

I want to create billing document using VF01 transaction with the material document number created for the purchase order (also done in VF06 as background processing ) and add a condition type to the header conditions with the condition value .Are there any user exits for this purpose or do I have any other option to do so.

Any input will be appreciated.

Thanks,

Venkatesh.

Ph - 080-41561218.