I have one question, is there a way to undo the newly added subform record upon closing the form? The Customer Name can be saved in the Customers table, (because there was a prompt anyway), but can the same be done for the subform?
Not possible without some really strange code. As soon as you make a different selection in the combo, the CURRENT record is changed. You are not moving to a different record. You are changing the current record.
I don't care what your boss says, you need a separate UNBOUND combo for searching.
You would need to save the PrimaryKey value of that record. Do you have it saved somewhere? If so, then a simple Delete query with a Where clause will do it. I don't know exactly what you have at this point or I could give you more specific instructions.