User exit / BAdI to change the Availability Check

Hi Experts.

I would like to know how or where can I tweak the standards so that when I create a Delivery like from Transaction VL10B, I can change the availability check to 'Z4' on which in this avail. check, it includes the use of restricted stocks from restricted batches.

I've tried a BAdI in IF_EX_LE_SHP_DELIVERY_PROC~CHANGE_DELIVERY_ITEM and created a condition:

If the the delivery type is Replenishment, CS_LIPS-MTVFP will be equal to 'Z4', but the delivery being created does not create batch split.

I debugged and it goes to the BAdI and changes MTVFP. I might be missing something or the BAdI used might be incorrect. Could you kindly help?

Thank you in advance. I'll give reward.