@anomaly13-
I don't have a definitive answer so take this as speculation.
Removing the device from your account on my.roku.com should prevent it from accessing your Roku account. This should prevent that device from accessing any premium subscriptions you have taken out through Roku.
Any premium subscriptions you have directly with the channel will still be accessible via the login credentials you established with that channel. I suspect these will not be retained on the device, but I don't know this for sure. To be sure, I'd suggest logging into any such account on its website. On many of them you can remove linked devices. On all of them you can change your access password.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X
