Sure you can attach another roku to your roku tv, you can even set the roku tv to tune to hdmi the new roku is using skipping the roku tv home screen for the newer roku home screen. Of course the stand alone roku won't have input tiles on the home screen like the roku tv does. You should be able to switch from one roku to other be just pressing the home key on the remote for which you want to control, pressing home on the other remote should switch you back. I would make sure each roku is set to a different theme, and turn off the seasonal themes in the settings menu of each roku.
Edmund
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.