If you mean that you want to purchase a smart stick to replace your nowtv box, then yeah that should be no problem.
When you setup the new smart stick, just use the same account details on your older box.
I plugged in my nice new stick and put in my account details but when I ttried to watch a film on my account, it said I needed to subscribe to be able to access films. I already have. What's the problem?
When you go to My Account > My Passes on here using your internet browser does it show you have an active cinema pass ?
If so, log out of your new smart stick and re sign back in with the same exact details that you double checked your pass above.