How to write Custom logic in transaction variant- SHD0

Hi All,

I am working on vendor master creation by replicating MK01 transaction to ZK01 using Transaction variant(tcode:SHD0).

Apart from customizing the screens through transaction variant, I have to write some logic for the business requirement. Is there any way that we can write some logic in transaction variant.

I have to carry-out some validation on the initial screen of MK01 and I could not found any user-exit / Badi for this requirement.

Please give some approach on this .

Thanks

Mahesh