As a registered Shopify Partner - I am able to create "Development Stores" inside Shopify. This functions exactly like when you create a trial store - except that it has no time limit.
You can use a development store for testing or backup. For example if you want to test a new layout or different styling options - you can do this on your dev store without disturbing your customers experience of your live store.
Your development store will be invisible to your customers. And you can name the domain however you like.
If you have any questions about this gig or how a development store works - please message me!