To alter the incidence you are actually tipping the whole airfoil up at the trailing edge. Sanding just the trailing edge will not do it. If the saddle is a good fit to the wing then the whole saddle has to be sanded with more material being removed progressively towards the trailing edge.

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I would do that anyway. Why risk all that you have in an airplane on a couple of wooden dowels. Use four screws. It is then easy to make adjustments to the wing after some flights.

Ed S