Brian,
Good question. The engine limits are specified in the flight manual and are required markings, so the typical red lines must appear, in any piloting situation, per FAR. There is no approved way to show other limits, and the FAA guards against non-conformities (rightfully) so additional red lines are not allowed.
In the A model, it took a lot of negotiating to come up with the white region below 694 degrees, and I would wage that marking would not be allowed today.