To reroute and existing instrument track would still require splitting the instrument track. After splitting the track, setting the track input, the interleave would still be in stereo. By design, recent versions of SONAR no longer automatically change the interleave when audio inputs are changed.
 
The same is true when working with audio tracks in general. There is no longer a link between the audio input setting and interleave.

vdvorn

scook
Again, the interleave button is only available on audio tracks. Instrument tracks must be split to gain access to the underlying audio track and its interleave button. The split instrument function is in the Track View Tracks menu https://www.cakewalk.com/Documentation?product=SONAR&language=3&help=Views.03.html and the context menu in the track header.

If it is so complex, I can hardly understand how the interleave button relates to the topic and why Savoy mentioned it...

This bit is easy.
 
In Trck View, just right click the audio clip and select Convert to Mono, halfway down the list

This bit is easy.
 
In Trck View, just right click the audio clip and select Convert to Mono, halfway down the list




That is exactly what I have done (see my post), but the topic is not about getting to mono from stereo...

To go back to the earlier suggestions, this is where you can split an Instrument Track to Split Adui/Midi tracks which will give you access to the Interleave Button:
 

 
Just right click in the region below the buttons labelled "None" to get to this menu

Bristol_Jonesey
To go back to the earlier suggestions, this is where you can split an Instrument Track to Split Adui/Midi tracks which will give you access to the Interleave Button:
 
 
Just right click in the region below the buttons labelled "None" to get to this menu

Thank you.