TS,
Pls do yourself a favour. Relearn the basics of photography. It has nothing to do with which metering mode you set, it has nothing to do with most DSLR - in fact all SLR regardless of film or digital works the same when it is set to manual mode.
I know I am blunt but I just do not want you to learn the wrong things and not able to appreciate photography, especially when you such a wonderful piece of hardware - D700. The reason why the exposure metering changes is dependent on the setting you assigned to the camera's ISO, shutter speed and aperture setting. When in manual mode, you decide how you want the picture to be exposed. The camera will accept whatever setting you give, even it if means the outcome will be overexposed, underexposed or correctly exposed.
Experienced actual day wedding photographers are seasoned enough to know when the lighting condition changes - either due to the ambience lighting changes or he/she moves from one location to another - resulting in different exposure reading. As such, he/she will be quick enough to make chaneges to the camera setting to dial to the effects he/she desires. In certain instances, some photographers prefer to use aperture mode or shutter priority mode. A the end it all depends on our level of comfort and shooting style and the behavior of your camera.
It will take a while to appreciate manual control. You can practice shooting in aperture mode first and slowly moved to shutter priority to see if either of these modes suit you better.
Cheers,
Daniel