so i'm in middle of making mrs antigee's bike a bit more suited to the lanes and road commute it gets used for – but it has to be the "same as when you started" got some nice carbon riser bars exactly same angles/shape but about 40mm overall longer – now i've seen cut carbon bars for sale in the classifieds – do i just do it? and tips

Yes! Use a fine, ideally blunt, hacksaw blade, put some electrical tape around the bars to absorb the worst of the dust.

thanks – taping sounds a good idea to avoid any starting slips as well
finishes lunch and heads off to do carnage in the underground bodgequarters – cellar workshop

There's a certain blade you need in the hacksaw that has minimum of 25 teeth per inch or something

My local bike shop wouldn't cut my carbon bars due to some health and safety issues with breathing carbon dust so I guess it's wise not to breath in the dust or leave it lying around on the floor.

I ended up cutting them myself with a hacksaw and tape around the bars where I was cutting, didn't really seem any different from cutting non carbon bars.