I have no idea if the designers had any plan for how to change out the tops. My guess is they didn’t think it through that far because this whole concept seems

I have no idea if the designers had any plan for how to change out the tops. My guess is they didn’t think it through that far because this whole concept seems poorly thought through. If you were doing to change the tops, though, I would expect some external lift would do that job. Adding lift capabilities to the base or to the tops would add a bunch of weight for no reason. (Those extra tops have to be stored somewhere. Might as well keep the lift mechanism in the storage facility.) The obvious answer is that a forklift is used to put the top onto the base.