Add Custom Fields to Shipment Processing (VT01N-VT03N)

We have a requirement to add 10 new fields to the shipment processing transactions (VT01N, VT02N, & VT03N). They will all be header level attributes that will be included as part of table VTTK. It appears SMOD enhancement MV56AINI (function module exit EXIT_SAPMV56A_004) may be the only way that SAP has provided for this kind of enhancement to the shipment maintenance transactions.

I have reviewed the suggested approach supplied via our community pages (https://answers.sap.com/questions/2695020/vt01-extension---add-custom-fields.html), and do not have a clear understanding of how best to proceed. It seems as though the solution outlined is missing some critical details. Can anyone provide a link to more detailed information with regards to how to implement MV56AINI?

Kind Regards