Hi,
Sorry but I'm new on this, but is it possible to reduce the pitch on a pair of Mercruiser Racing cleavers 4-blade 17.5x32"??
and if so, by how much?

Br
Richard

You would be better off selling them and buying the correct pitch.

How far are you thinking of dropping pitch??
Assuming the diameter of the prop stays the same...generally 1 inch in pitch +/- changes the engine speed by about 150-200rpms +/-
there's really no way to change the pitch of the prop as its determined by how the angle of the blades meet at the hub....to truly change pitch they would need to be cut off and re-attached.
Now if you are looking to gain some RPM they have ways of doing that.
They can thin the blades for less rotating mass..
They can take cup out of the prop if its there.
They can cut the outside diameter of the prop down allowing it to turn faster
They can even bend the blades a bit to make sure they are actually all angled the same....
A good prop guy will be able to point you in the right direction with what your goals are...