Depending on the keg it should come off with a bit of careful levering. I've accidentally done it a couple of times myself and never had it actually jam on. In fact in some threads about doing weird things like purging sulphur out of a brew some people even suggest doing what you have done and bubbling CO2 up through the brew through the dip tube - never deliberately done that myself but you shouldn't be stuck. Is it originally a USA sourced or German sourced cornie? I know the German ones are a bit tight to put on sometimes but generally the two posts are very close in size. Also if you make a point of smearing a wee bit of keg lube on the posts every time, the connects work a bit more smoothly if you need to get them on or off in a hurry.
Glad it's all turned out well. Actually despite his misleading username I'm sure that Archibald will be delighted to know that there's a lad out there named after him.
Bit hard to see in the pic, but I wrote on the fridge the sides for beer and gas, then always put the kegs in the correct way with the posts lining up. With this fridge I don't have a lot of space on top to see into and knowing which posts are where makes it easier. The front 3 kegs are not too bad, it's the ones behind that are harder.