Great answer, Shiny. Essentially (and you have hit the nail on the head) we design spring hangers to support the proper weight load at any given location in the operating case. The hangers are installed on cold piping that is restrainted to a theoretical position. If they are variable hangers, the theoretical cold load accounts for the movement to the operating position, and so does not match the required support force to restrain the pipe.
But, if there are a significant number of variable springs (or if the weight of the pipe, valves, and insulation is not as the analyst assumed) the pipe will self-adjust its own position so that the weight is exactly equal to the sum of the support forces. This will cause many variable spring supports to move to the actual installed position.
Pipe stess software is remarkably good at calculating this actual installed cold load case, but unfortunately nobody can provide you with weights for valves and piping that are sufficiently accurate to design a lot of spring supports and have none of them move off the theoretical cold load when the pins are removed.
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CraigB