for anyone else landing on this thread trying to figure our how to get the barrels out of GS Aventure cases to begin the re-keying process- i just figured it out...
You need to push the little metal tab that protrudes from from the side(perpendicular to axis of rotation)of the barrel in the back inward(toward axis). It's hard to see in behind there but once you hit it it's easy. I used a knife tip. With the key in, pull outward on the barrel as you press and they'll pop right out.
Then follow the tumbler shuffling process, the same as the vario cases listed before.
Hope that saves someone a little head scratching!