Adjusting the vertical alignment on the 7 and 7s in principle shouldn't affect the horizontal alignment. Yeah, in practice it usually does, but that's just because the adjuster is kind of touchy.
What's going on inside:
-- Horizontal: This adjusts by a screw that bears on the horizontal arm that carries the rangefinder mirror, same as on older Canons.
-- Vertical: The rangefinder mirror sits on a little stainless-steel spring. Turning the adjuster jacks this spring up and down, changing the mirror's vertical alignment. The adjustment is touchy because you only need to move it a VERY small amount, and because it jiggles on the spring as you adjust it. That jiggling can change the "set" of the mirror enough to vary its horizontal alignment somewhat. On the other hand, sometimes you can make an adjustment to it without changing the horizontal alignment at all.
Once adjusted, it should stay adjusted throughout the entire focus range, because the whole business -- mirror, spring, jack screw -- is rotated by the lateral arm, so all the parts stay in the same relationship as you focus.
Note, if you are lucky enough to own a 7sZ, that its vertical position adjuster is NOT the same! I don't own a 7sZ :-( and have only seen pictures of the innards of one (thank you, Peter) but it appears from those that the 7sZ uses a different type of vertical adjuster -- a cylindrical prism located transversely in the light path, pretty much like what you'll find in a Nikon S2.
With this type of adjuster, turning the prism moves the image in a circle, so adjusting the vertical alignment definitely WILL affect the horizontal alignment. The advantage is that it's much less touchy to adjust, and doesn't jiggle as you're trying to adjust it.
