Removing and reinstalling barcon shifters is very easy.

Removal:
Shift to the position where the gear wire is at its slackest
Unscrew the large screw with a coin or very wide screwdriver
Dissassemble the lever parts.
Unscrew the recessed hex key screw inside the shifter BY TURNING IT ANTICLOCKWISE!!!! (5mm hex key).
Pull it out when loose

Installation:
Remember to turn the hex key THE WRONG WAY to tighten the shifter. Do not tighten excessively, I believe I have heard reports of people stripping the threads, but may be wrong about this,

This is good easy experience to gain, My barcon recently loosened on the road but it's an easy fix... just remember to turn that screw the wrong way

I have used soapy water on occasion to help handlebars through the stem, but don't know if this is "correct".

EDIT: I'm referring to the Shimano Dura-Ace barcons... other makes/models I have no experience of.