Ted here from Shopify, thanks for reaching out to us!
This is a great question! So it's not possible to change the store manually if the store is for sale with Exchange. Instead though, if you contact firstname.lastname@example.org directly our Exchange Support can help you edit the store name.
How are you finding Shopify so far? If there is anything else I can help you with, please let me know, I'm happy to help!
All the best,