What a wonderful question!
I believe that the special rules (6th edition lesson manual 11.5) (EBAE XVI.47.f) for the short-form word friend would be used regardless of whether it was a proper name or not.
See also (EBAE XVI.47.b) - The NOTE to this section is on the next page (Page XVI-4)-
EBAE XVI.47.b Note: Short-form words which are common words are not to be considered as proper names when they appear in names of books, articles, chapter headings, publishers' names, etc.
Society (of) (Friend)s
MY (FRIEND)LY (EN)EMY.
You can see that the short form for friend was used in both of these examples.
I hope this helps.