The Shifter Components are not typically that generic. They usually represent a body part. (as far as I understand.)
Rigging a template and then importing is a valid approach. I do that for my eyeball rig.
But more often, I build it in a POST script. For example, here is how I build a control ribbon for my eyebrows: Eyebrow rigging
So I am using mgear.core.curve.addCnsCurve() to build a curve that is constrained to a list of transforms. (But then I loft it and use follicles ultimately.)
Also, you can make your own custom modules. I have only ever copied an existing module and edited it. But then you can save it anywhere you want, and point to them in your Maya.env file with the following line. Then they will show up in your list of components.
MGEAR_SHIFTER_COMPONENT_PATH = P:\YourFancyPath\tools\mgearCustomModules
So I keep a separate git repo of my custom modules. And if they ever get good or useful enough, contribute them back to mGear!