Well the title really says it all. This is a function a lot of editors possess and in mp3tag I am constantly trying to use it, failing...
I figure it wouldn't use much work this is why I dare propose it.
Please see the documentation on keyboard shortcuts:
You will see that Shift+Enter is already taken.
Check the fields that had the focus on whether they now got added custom values.
Thanks for your reply. Sad, but it is what it is. ("...add the contents of the current Tag Panel field to the list of custom list values for that field..." - I have doubts as to whether any one person really ever needed this particular command and especially a short cut to save time with its execution but it is what it is).
I can master only 3-4 shortcuts per programme and these tend to be really popular commands.
Shift+Enter in MS Word (and Excel and most other office programs) creates a line break, for instance. So it seems to be local to the application.