The jobs you mention are well within the ability of even the most basic mechanic, mate. Switch is a straight swap job, pull out the multiplug at the fusebox end (on later models, I'm guessing 23's are the same.)
Again chain and sprockets are a p.o.p, gear lever and speedo drive cover etc off first, with no paddock stand one work around is to crack the spindle nut and front sprocket nut off first, then leaving the bike on the sidestand you can get away with a trolley jack with a block of wood under the exhaust collector, the bike should lift albeit at an angle, as long as you keep clear of underneath once the rear wheel's off the ground. Try at your own risk.
If the chain is 'endless' ie no split link, you'll either need a splitter or grind off one of the links where they are peened over.
This it?
, my cousin lost his job and gave me his bike. It is a 1989/90 CBR 400RR NC23. It's in need of a bit of attention as he did not look after it, what a fool! Now i have bought a few parts already for the bike of ebay, just to get it mot ready , as well as some others its in desperate need of. (Service Kit, chain & Sprocket, Ignition barrel & tank lid/lock, Grips, KMH to Mph overlay, Throttle cables, choke cable, full set of Brake pads, sump plug hmmm think thats it lol, Now i was a car mechaic for 2 years and im prety compitent however is it easy too replace the chain & sprocket, ignition barrel? I dont have much too play with as i have a holiday too pay for as well as tax n mot :O Anything i should worry about or hard too do regarding Chain n sprocket or ignition barrel ? I dont have a padock stand iether 
and ideas? I will put a pic up :) thanks nick
sweet!