Once your song has been published. Its gone. You have lost control of it.

Anyone can sing it with different words and a different tune.

If you're lucky enough to make a commercial recording, the guy who is putting up the money has the right to effect what changes he wants to make it marketable. He'd be a fool to speculate his company's money on any other basis. In which case - you've lost control before the public have had a sniff of your creation.

These are the harsh facts of being a composer.

Of course this presumes that anyone is interested enough to listen to your creation in the first place. if no one gives a shit - you can have as many delusions of grandeur as you like.