Username, email autofill and custom title

Hi champions

I am using woocommerce checkout.

I have set it so customers need to add their username. But it autofills with email address, and I can’t have this.

Also, I want to add a custom title for the username form. Instead of Account Username, i want something like: Your anonymous Username

I don’t want it to autofill with email.

I am using storefront theme.

Can i use a storefront child them and edit the functions.php?

What code would i enter in there?

Thanks

Steve