Enhance FM:SD_F4_EXTENDED with new custom fields - 2

I saw the question at https://archive.sap.com/discussions/thread/3700486 and have followed the instructions to get the custom field to display on the screen. However, it isn't clear to me how to get the form Shipments_Read (RV56TRSL) to use the new custom field when selecting from VTTK without doing quite a few modifications to add my new custom select-options to the parameters of shipments_read.

Are there more enhancement steps I need to perform to get this to work correctly?