Glasses with cyl come with 3 values: SPH, cyl and axis.
SPH is the main diopter, cyl is the added diopter at a certain angle only, and axis is the angle, so that stays the same (the axis never “reduces”).
The walk down to zero correction can’t be planned ahead, but basically there are 3 options.
Keep the SPH and cut the cyl completely
Works best if your cyl is only 0.25 or 0.5, may work up to 1, especially if the cyl was overcorrected, too.
Above 1 it most probably causes serious challenge to the brain, so better choose from the other 2 options.
After a few SPH reductions (when keeping the cyl unchanged, both strength and axis), once you feel you have some practice with reductions, keep the SPH and reduce the cyl by 0.5 (or maybe just by 0.25). Then do SPH reductions again, and when ready, reduce from the cyl again. This is the most standard method.
Increase SPH by half of the cyl dropped. This means you are not really reducing the overall strength, just on the sph - cyl difference, but you are simplifying the complexity of the glasses. If the cyl is high, don’t drop it in one step.
The thing with cyl is that your brain has a much more active role with composing the correct image from the eyes’ inputs. So it will need time and patience to let the brain adjust instead of the eye corrected only at a certain angle. It can easily take 3 times longer than a simple SPH reduction. Be prepared to tolerate failure, you may be stepping back and forth before you can really drop from cyl.
As for normalised and differentials, the most common is to keep the 2 aligned, so yes, you will not be able to use the early differentials as normalised later. This is why some people drop all cyl in one step at the beginning and walk the walk with simple SPH only.