No. It has nothing to do with avoiding "collisions".
The sensors always transmit on the same frequency. The only thing that prevents a collision is timing. Should a collision occur, that data is just lost, and you have to wait until the timing drifts enough that the signals don't collide anymore.
Also, you have to consider it's not just Acurite's sensors you have to worry about, but any device transmitting on the frequency.
Fortunately the data lost to collisions isn't a big problem in most cases.
Ok.
So what exactly is the purpose of the three channels, if the frequency is always the same?
My understanding is, that each channel is a few kHz off from the others, so if you do have something
in your house that transmits on the same frequency, you can dodge that.
I think the manual too states, that if you're having connection issues between display and sensor array,
to change to a different channel, because something else could interfere on that same frequency.
And also, if the two sensors transmissions collide, the rain gauge would miss counts I think.
And if the drift is very little, you might not get anything for hours until the timing drifts apart far enough.
I personally would want to avoid that at all cost.