"$CURRENT" is very limited in these situations as it can only be applied to one item at a time, and you may want to pose several Mags, Bases, and Zones at once.

Quote - ...is it possible to make a pose file that can change the magnets value.

Yes there is no problem with that. With the magnets attached to a figure and set as desired, just save a pose and use "Select subset" to exclude everything except the magnets. But note that Poser does not save scale data to a pz2 (pose) file. If you want to include scale data you have to edit that in by hand using a text editor.

A quick and dirty alternative to the above is to save the magnets to a pp2 file using "Select subset" to include all Mags Bases and zones, then rename the file extension to pz2 and move the file to a pose folder. The disadvantage to this method is that the resulting pose file will contain a lot of unnecessary junk that is not needed in a pose file, but it does work. An advantage is that it includes a some stuff that would not be included in a pz2 file saved from the Poser interface, for example scaling, parenting, and "deformTarget" (which actors to affect).

When using poses on magnets it is best if the Mags Bases and Zones have unique internal names to avoid conflicts with other magnets that may exist in the scene, and to avoid problems with the automatic name-number that Poser assigns. For example:

baseProp rCollar Base 1

magnetDeformerProp rCollar Mag 1

sphereZoneProp rCollar Zone 1

etc.

Note that to change the internal name you need to edit the file in a text editor or cr2 editor (eg CR2Builder), you can't change the internal name from within Poser.