This may be a stupid question but is it ok to cut down carbon handlebars in the same way that one can trim ally handlebars? Will the structural integrity of the carbon be adversely affected? I have bought a set of ‘chewy’ On One Knuckleball carbon bars that are too wide for me (760mm) & I’d like to reduce the width.

Yes, fine to cut them.
Don’t use a normal hacksaw blade though, either get a finer normal blade or a proper carbon blade. Carbon is DEAD EASY to cut, lots easier to get a nice finish than alloy, just go slowly and keep it lubricated (Water) to keep the dust down.
I can literally cut 1mm thick slivers of carbon when I’ve cut a steerer a tad too long (better then too short…)
You’ll be fine. 🙂

http://www.parktool.com/product/carbon-saw-blade-csb-1?category=General%20Shop%20Tools

A hacksaw blade with a tooth count of 26 tpi and higher is fine