Spacing can be re-measured with the clamp in place, but if I re-tighten the strings enough to check the alignment, I'm afraid the tension will pull the neck forward and mess the spacing.
The neck alignment can be checked and adjusted without having the strings on by using a long steel rule held against the side of the neck (edge of the fretboard). It gives you the same information just from a different point.

If you picture the steel rule as an extension of the neck running through the body, you can measure the relationship between the steel rule edge and the bridge, E saddles or even the bridge post holes.

Also, if aligning with strings, they don't require any more tension than to take out the slack. You can even use fishing line or baking twine for this purpose. In fact, as a quick check, I've done it simply by holding a string with my fingers across the E nut slots and the E saddles.