Custom value lists cannot be exported. You'll need to add a table and set up the values to be drawn from that table.
You can add a script that replaces your Edit function and either place an "edit" button next to the field or include "edit" as a value in the table and use a script trigger to detect when this value is selected.
Your script can change to a layout based on the table of values or which displays a portal of the value records for editing. This can even be popped up in a small floating window much like a small dialog box.
I was afraid of this. It seems like a logical thing to be able to export and import custom value lists. Why? Because they are so convenient to create and the modification feature is built in. If one could dump/restore these types of lists it would save programming time (in my case anyway).
Thanks for your reponse. I will implement these lists as tables.