We have three Roku devices and three remotes in the house. One of the remotes is turning on another TV in the house. Is there a way to program the remote so it has a unique code and will only turn on one TV?
That is happening because the IR codes that Roku uses match some other TV brands. Vizio is one example. No, you cannot alter the IR codes used by your Roku nor what your remote emits.
Some Roku remotes do have the ability to control TVs, and you can set the code they use. But that won't help when the Roku and the TV use the same batch of codes. And there's no way to change what codes are used on either the TV or the Roku.
I have that problem myself, in that I use a Vizio TV as a computer monitor that is near one of my Roku TVs. What I had to do is shield the IR receiver on the TV so the Roku remote doesn't affect it. That works for me, since I don't actually ever need to use the remote on the TV. Because it's used as a monitor, it's on full time and the input is always the same.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
To stop the Roku tv from controlling your non-roku tv you can switch to wifi remote, an abandon the IR roku tv remote. You can't stop the non-roku tv remote from controlling your roku tv, because the roku tv will accept both IR & Wifi signals at the same time.