How to add Employee Search to MES Employee ID?

I am trying to enable Open With functionality on the Employee ID field but I’m getting some odd behavior here. To my custom MES Menu screen I changed a label and added a LikeValue on the EmployeeID field which is bound to MESControl.EmployeeID. ( Using Data Tools > Custom Column Like I set it to like EmpBasic.EmpID).
After saving the customization the “Open With…” feature worked quite nicely. But after closing and reopening the same customization the feature was gone. The label change was there though so I know I opened the right customization.

Previously I tried using Extended Properties to add a like value to MESControl.EmployeeID but the table is not listed. Is this field locked down too tight to change? Or am I missing a step?