It can sometimes be necessary to use a particular pronounciation of a word -usually the word ending- in order to preserve a rhyme-scheme.  That doesn't have to involve affecting a fake accent, which is best avoided unless you particularly want to insult people.  Pronounciation and accent are two quite different things, and with a bit of thought such things can quite easily be managed.  Singing in a language foreign to you is another matter, of course, and should never be attempted unless you understand that language sufficiently well to conduct a reasonable conversation in it.