It used to be possible to view the source of a CoreScript it is linked to. Not sure if it is anymore. If anybody knows, I would appreciate the help! Hmm.. Not sure what tags this fits under. Might work with Hierarchy.
You can view the internal-code repository here:
A corescript doesn't have a source property, but it does have a LinkedSource property, which links to an asset you can view in studio's browser.
Never mind, I figured it out. Copy the LinkedSource into the LinkedSource of a normal script.