As long as you are using the in-camera meter, the only thing you have to adjust for is the movement's effect on the lightmeter. Any exposure changes from the extension tube (magnification) would be "seen" by the in-camera lightmeter, so no other adjustments would be required. I've done this (with the old 24TSE). You can focus right up to the front element!
I think exposure adjustments are minimal for most movements. The extension tube moves the lens away from the film / sensor plane, so the image circle gets even bigger. It is easier to just look at the histogram and adjust if necessary. I found that even with film bracketing was the only real way to go. The whole metering problem with movements is because the mirror & meter do not see the same image as the film/sensor plane. But if there are bright and dark areas in the scene, then you don't really know which part the meter is seeing. The meter could under or over expose the scene depending on what areas of the image are missing the meter but hitting the film/sensor plane.
Dave