If it were mine, I would rebuild the assembly, and have it ready as a bolt on replacement if the need arises.

The official answer is you are not supposed to swap skegs. The unofficial answer is I have done it 1, 2, maybe 50 times. The motors don’t really seem to notice I promise. Swap the skeg, don’t bother with that one, and away you go.

In regards to the gear swap, you need to swap the whole fwd/reverse/pinion/clutch dog/prop shaft assembly. But, I would just rebuild it and reseal it and have it ready to bolt up should you ever need it. Wont be a waste of money by any means.