How do I change my Wildcraft or just turbo rocket username/nickname to a different one without erasing..

How can I leave my name blank and just empty

To change your name that other players see, go into multiplayer, and when you're in the place where you can see which game world it's on, and choose whether to join a game or make your own, there's a place that has your current game name. If you click on it, you can change it.

If you're wanting to change the name of one of your animals, simply go into their personalization menu, and at the top of the bar of things to change about them is a paw print one. On it, you can see their name and gender. Just click on their name to change it. I hope this was helpful!