Change theme for subdomain only, keeping everything else as it is

[RetroShirtsMan]

Hi,

Is there a way to add a subdomain (done that already) and then changing the theme only for that subdomain?

What I want to do is, running a beta subdomain "beta.myshop.tld" and configure a brand new theme there for the people to test it kind of "in production". But I don't want to release it on the main store before testing...

Everything else, like products, collections should be exactly the same as in production. It should even be possible to purchase on the beta site. 

Of course, I will also manually exclude it from google to prevent DC issues...