OK, I tried Programming an unused button by turning on the recorder, then click.....
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Tivo-2 button (that's where I have the command that goes to the Tivo menu)
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Then my Tivo button (that tells the TV to go to that input)

When I save it to the remote and try it, all it does is mutes the TV volume. Weird I know.

I have also tried going to the first button, copy the command to an unused button and then go to the second button and copy that command into the same unused button, saved, tested, nothing.

On a regular remote what I would do is....
Push the 'Tivo' device button, then menu. Then scroll through on the 'Input' button (which I have pushed through from the TV to Tivo) until it gets to the Tivo.