Can you switch calibration off?

Hi

I'm thinking of going from a PC to a 27 ins iMac. Would try to profile it with Spyder 3.

This would probably result in a darker screen, and I wonder if it is possible to switch back and forth between calibrated for photo editing and normal for normal viewing? (I can do this with my current Samsung monitor)
Any ideas about this?
Cheers

Yes it's all under the display option in settings.

Many thanks for that.
Cheers