Any question answered...

In an internal combustion engine if you shortened the connecting rod length whilst increasing piston height (for a total of no net difference) would that increase displacement, or would it remain the same

Displacement is bore² x stroke x π/4, so you have to change either the bore or the stroke (i.e. crankshaft throw) to change the displacement. Shortening the rods will change the side load on the piston and slightly alter the piston speed and acceleration curves, but it won't change the displacement. Raising the piston height to compensate for shorter rods is wrong - you should reduce the barrel height instead, otherwise the gudgeon pin is too far from the action and the piston will tend to rock more.