You can move them between springs. I've done it multiple times. You just need a little elbow grease. Tire spoons are a good tool to use for prying them out. Not sure why airlift told you that.
This is however a reason that Firestone air springs are better. Firestone are narrower diameter and don't expand into the coil open areas as much as the airlift. So they don't cause spring binding like the airlift ones. The result is a better ride when empty vs the airlift. (I have both sets and I've also run GX air suspension for a while, so I have some pretty good direct comparison experience).