Nick here from Shopify.
Just to clarify, are you referring to the title of the theme? You can change the title of the theme in the Admin > Online Store > Themes > Action > Rename. I took a screenshot where I am referring to which you can see below.
Can you let me know if this is what you mean or not, please? If it isn't, would you be able to go into more detail of what you do mean in a reply to me?
All the best, Nick
No problem at all. 🙂
Can I ask what you mean exactly when you say theme marketplace? Unless you own the theme or developed it yourself, you wouldn't be able to sell or profit from it in any way.