What PhilC said about creating a full body morph (FBM), is the correct way to create one.  However in the context of this thread it might seem to suggest that saving a Full Body Morph will save the influence of the magnets. It wont!

Creating a Full Body Morph, won't save the influence of magnets. This is because 'Create Full Body Morph' does not really create a morph, it just makes a master dial/channel to control actual morph channels in the individual actors (body parts), and injects slaving code into expressed morph channels to link them to the FBM channel.

Before you can save a correctly functioning FBM, you need to create the constituent morph channels in the individual actors to be affected. You would then set any morph channels that you don't want included in the FBM to zero, and any morph channels that you do want included in the FBM to a value of one, or some other desired value. Only then would you use Create Full Body Morph.

Which version of Poser are you using?