Sorting/Editing Custom Field "Dropdown Multiple"

[Callahan78]

I have a Custom Field "Dropdown Multiple" that I want to expand from time to time. There will be between 20 and 30 entries. Now I would like to have the entries sorted alphabetically.
Is there a way to achieve this?
Some possibilities could be:

• insert new entries between the existing ones (instead of appending them at the end).
• moving the existing entries
• delete all entries at once and insert a new (updated) list (bulk import)
• it will always be sorted automatically (which would be the best variant)

Unfortunately none of these approaches seems to be possible . . .

Does anyone have another idea?