You can do that but have to be careful to shape the edges accurately without gouging the foam. Or add the LE and TE caps after; that's what most people do. To preserve the balsa sheeting during the sanding process, add a piece of 2" wide masking tape aft of the caps directly on the balsa sheet for protection. You still will need to use care

A better method is to feather cut the TE and run the balsa to the edge; a small 1/8" cap may be used and feathered. Ailerons are cut from the wing, preserving accuracy of the airfoil and producing the best flying possible

The LE could be done similarly but that's a more advanced technique where a balsa sheet is first molded around the LE to shape it, then sheeting could be done as usual. What you want most is accuracy between the two panels so that the plane could fly the best it can