Aging Sweet Cider

I transfered my cider to a keg for bulk aging, I am using the keg for a number of reasons. My question is, should I back sweeten now, or wait until it is done aging to sweeten?

I always bulk age myself. I would not sweeten before aging though unless I added sorbate or something to stop fermentation or you will just keep running up the alcohol content. I never add sorbate to my ciders and have found that with repeated racking over time most of the yeast will settle out and you will end up with a perfectly clear cider, though there is probably some yeast left in suspension. However, I have never had a problem with fermentation restarting after long aging. Most of my ciders will be aged for almost a year before I bottle them. It is easier to do when you have many batches going at once. The temptation to drink them early is lessened and I usually end up with a better cider.