Kerry,
I think some of the early Citroens had a provision to add nitrogen to the accumulators to adjust the ride quality. Rebuilding is different because the accumulators usually fail due to a rupturing of the rubber bladder that separates the gas from the fluid so they need to be split open and resealed, not an easy job. Besides, you'll want to replace not repair your accumulators and keep the old ones because once you remove the mounting brackets they make great Bocce balls.
LRG