That's the beauty of it, it's your product and you can do anything you like.
I've got to address my earlier statement for rewrites. When you first put a song together it's at a delicate stage and full of energy and inspiration, and that's what makes it work. Wholesale adjustments then could kill the whole thing if you're writing solo. I'd say at that point, after a day or two, you'd want to take a good look at the melody against the chord structure and play around with some alternatives and then take a harder look at the lyrics and make sure your ducks are in a row.