I think this would most likely address your specific needs, but not necessarily the expectations of all other users — some of which simply expect Mp3tag to not alter the data displayed in the edit field.
I've thought about auto-translating the LF (and single CR, which also exists) and translate it back when saving, but this also prevents users from changing the linebreaks to their desired format.
I think for now you need to resort to the approach suggested in this topic to replace the linebreaks to your desired format. And if you want to have them correctly displayed in Mp3tag this would mean CRLF.