Has anyone ever add a subtab to the General Preferences page in order to group their own custom parameters?

Only Bundles can do that but via Field Group.

Really? How so? (If your able to show/explain)

If the parameters are part of the bundled script(s) and of Company type, they show up under General Preferences > Custom Preferences tab (if I recall the name correctly)

Ya, I got that. I'm asking can I create my own subtab in General Preferences (to house these parameters)?

You cannot.