Can a I modify the template on which a Project Area is based?

This question refers to quality management and project templates - I can provide some information about project templates in general, hopefully someone from the Quality Management team will address the QM side.

If you modify a project template any new project areas created from that template will have the modifications but existing projects will be unaffected. If you want to create a variant of a predefined template it may be better to create a copy of the original template by exporting and then re-importing it rather than modifying the original. If you want to be able to make modifications to your project configuration in a single place and have those changes reflected in multiple project areas you may find that process sharing is a better alternative, I don't have sufficient knowledge of QM to be able to answer whether the change you want to make can be accomplished by editing the configuration or if process sharing could accomplish this effect.