Templates should expose their master page's public properties so that they can be changed in the template designer.
An example would be a public property call HeaderImage. With this public property you could then change the header image anytime updating the visual look on a regular basis easily from the backend.
Overridable Properties in Instance Pages
These public members in the master pages explained above should be exposed in the designer for page instances that are using the templates. As an example you could override the HeaderImage public property on a per-page-instance basis. This would eliminate a whole lot of custom user control development. It is a natural fit for the architecture and a great time saver for the developer.
Thanks, I hope you add this to 4.0.