A user-friendly way to modify the contents of a pop-up menu

In the system I’m currently writing, there is a need for a large number of pop-up menus to save time and to ensure consistency of data entry. The user (who’s not computer savvy) then needs a user-friendly way to modify the contents of the menu. My solution to this has been to provide two data entry options as below:

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If the desired value is in the menu, it can be selected (and it will appear in both boxes). If not, it can be manually entered in the adjacent box (and the pop-up will be empty). The user can then, if she wishes, click on the little plus sign icon to add that new value into the menu permanently. Similarly, she can select a value from the menu and click on the minus sign icon to permanently remove that value from the menu. The menu contents are stored in a separate database and are extracted at start-up - it’s actually this database that’s modified when the user changes the menu content.

I’d be interested to see any alternative approaches to this task.

Another strategy is to have a menu selection item for adding a new item; could be at the top or at the bottom of the list of options. Then the procedure handles that selection.

True, but my objective is to make it as simple as possible - this way everything is in the one place - no menus to remember. Also, my client has never used a Mac before.

I was thinking of a pop-up menu like this:
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which could provide a text input dialog for adding or deleting a choice, like this:

That’s simple enough, eh? You asked for an alternative approach. You may still prefer the original, of course.

The augmented pop-up is a very good idea but I’ll probably stay with the current approach simply because there are so many instances of it. Thanks Tom.