You can use any name for your developer account and Itch.io allows you to change that name. There is a link next to the name: Change my username.
You can use your future name as your display name, or you can create a unique name for your game business.
You need to use your legal name for the tax declaration. If you officially change your name, or start trading under a business, you'd need to contact support and ask to retake the tax interview at the time you qualify for a payout (if you're using the method to let itch.io collect the payments on your behalf).