In article ,
wrote:

Can this basic input impedence be adjusted? Should it be?

Sometimes, but that's usually a "service adjustment and repair" sort
of thing, not something that one is usually expected to do during
normal use. In a lot of scopes there's no adjustment that doesn't
require e.g. unsoldering parts.

There's enough variation between types of scope, that it's probably
most common to have a set of probes for each scope. Pick (and if
necessary adjust) the probes to match the input characteristics of the
scope, and then don't fiddle with 'em.