I've recently taken apart a shimano mech - not my bike so don't know the details but think it was LX - not shadow.
on these there is a hole with a socket screw (aka grub screw) that can be removed - the top of the hole is peened over to prevent the screw from coming out but this does nothing to prevent the screw being unsrewed by an allen key.
why am i telling you this? simply bechause the enitre cage mecahism, including the sring can be taken off, so if other mech designs are like this, you should be able to swap the entire cage over on mechs of same model i.e. fit a different length cage.
if you are thinking of saving weight by fitting a shorter mech, don't bother
i replaced a long cage SRAM X0 mech by medium and the weight saving in grammes could be counted on one hand.
also check ebay for carbon cages and alloy or CF jockey wheels - a more cost effective way to save weight.