Just be careful you don't let these get too heavy. The heavier the assembly, the more stress the pin will create, on the wool. You might want to iron on a patch of some sort, to the back side of the front apron, in the area of the kilt pin, to reinforce the fabric, if the pins get heavy enough to separate the weave.

Myself, I'd prefer to add multiple lighter pins, rather than a single heavy pin.