Shielding causes capacitance. Capacitance can form a filter
which can filter out highs. Depends on the application. Best bet
is to try it and listen. ToN gave the main way it could affect
tone. You can look up the formula for factors that affect
capacitance. Among them are area of the plates forming the
capacitor, and the distance between the plates. If the area of
the plates gets larger, capacitance goes up, and if the plates
are placed closer together, capaciance goes up. It's a bigger
concerned with shielded cables, where the insulation between the
shield and the center conductor forms a capacitor, and the
"plates" (the 2 conductors) are fairly close together. But
shielding in guitars is usually a matter of shielding the
control and pickup cavities. The area of the shielding could be
huge, but the distance between the shield and the rest of the
circuitry is huge by comparison to a shielded cable. I think
it's a non-issue. People realized what I described, but didn't
put numbers to it, look at where the "hi