On limit screws - on lesser derailleurs, the high gear (small cog) limit screw is usually labeled "H" and the low gear limit "L". On better derailleurs, I think it is assumed the mechanic knows and frequently they are not labeled. To find out which is which, screw one screw in two turns. Now pedal and shift. Note which cog you cannot get into.
As said above, cassettes/FWs on different wheels often do not exactly line up with the previous. Making the switch might be as simple as screwing in the "L" 1/4 turn and the "H" out that same 1/4. Once you find what your wheels need, doing the switch without issues can become simple. (Now, bikes have enough vagaries that I could be totally out to lunch.
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Edit: I hadn't heard of FB's shimming to make wheels consistent but it makes sense and I like! I raced with close to Japan's finest; identical hubs and freewheels BITD and did the swaps, training to racing and back doing nothing.
And funny because it is a little related and I just did it. How to make thin spacers. (The shop I went to had only 1mm ones.) I took aluminum sheet, nailed it to a piece of plank, secured the plank under my drill press, hole saw drilled the ID then did the same with the OD. So easy I made four. These to use on a fix gear where I am running the cog flipped so the cog surface butts up to the spokes. With a low flange hub and 19 tooth or larger cog, just fine but smaller cogs require spacers to keep the chain off the spokes. I want it dialed in to the bare minimum to allow as many lockring threads as possible.