Depends why you're singing the song - if you're singing it as a historical record set in a historical period, changing the words is dodgy, because you are in danger of falsifying history.
But if you're singing it in the first person, so to speak, rather than in character, and it's a song through which you are expressing yourself, there's no reason you shouldn't change it so that it says what you are trying to say. Words change, and songs change with them.