I was corrected a few times not to use an indefinite article in phrases like "Ich bin Studentin" and "Ich bin Japanerin," but have just come across the Preußenlied, which was the national anthem of the Kingdom of Prussia and starts with:
Ich bin ein Preuße, kennt ihr meine Farben?
Die Fahne schwebt mir weiß und schwarz voran;
daß für die Freiheit meine Väter starben,
das deuten, merkt es, meine Farben an.
So if I am corrected again, can I say, "Solange Leute 'Ich bin EIN Preuße' singen dürfen, darf ich EINE Japanerin sein"?
UPDATE: There have been questions on this SE about similar phrases, but my question is specifically about this particular song. I'm looking for an explanation of why the indefinite article is used there. Does it introduce a flavor or connotation there? If so, how? How do native speakers perceive the starting phrase of the song?