Anything that causes resistance to the sound waves traveling through the bore of the instrument will affect the way it sounds.

Think about a Harmon Mute on the end of a jazz trumpet...

Now granted, that is on the END of the instrument, but it still greatly affects how the sound wave travels through the instrument.

Take a paper towel roll and put ONE paper towel folded up vertical inside the tube... now place it inside the bore of your didgeridoo.

It should reduce volume slightly, reduce vocal clarity, and most significantly it will lower the fundamental pitch.

Groves, twists, and other surface irregularities within the bore definitely affect the sound.

Best way to experiment is start with a straight pvp pipe, record the sound it makes, and then “craft” an instrument by flaring the bell, placing bends in the shape, and introducing small (or large) objects into the bore.

played heaps of naturally hollowed out real didjs
with bends and had plenty of vocal clarity.
just remember it is the players skill level that plays a big
part of a didj being a good one, as much as a didj being a good
one or one that apparently has the vocal clarity affected because of
a bend.