The speed mod fairing (like the Knots2U one) requires an STC and 337,
so
it's a not the same as removing/replacing an existing OEM fairing.

Actually, only the original installation requires a 337, because a
major alteration takes place. After that removing and reinstalling the
same fairing is preventive maintenance.

There is actually logic to this (pretty rare for the FAA) - the
original installation requires a change to type design. It may require
new fasteners, changes to the mounting points, whatever. It makes
sense that it's not something an untrained person should do. But once
the original installation is done, taking it off and putting it back on
is no big deal.

In general - you would be surprised at how much the owner can legally
do, provided he follows the proper procedures.

Michael