User Exit for MIGO for batch

Hi expert

I am looking for user exits .at the time of migo when batch is generated into want the batch field to get grey, so the end user wont able to change the Batch no. and i want the grey field to be done for certain material. like ROH

Can anyone of you suggest me a more appropriate User exit to work on. Please dont give me a list of user exits out there for migo as I have seen all those in Different threads.

Thank You.

Nabil