Any way you go about it, you're going to have to do some figuring and a little alteration to either the badge or the kilt. Here's my throw-in:
If the badge is never again going to be worn as part of a uniform, and if the only use it will see is as a kilt pin, and you're probably the only one who will use it, then I think I'd go ahead and cut the post off of it and solder on a big safety pin. That might cut down on some of the weight, you'd have an item that you can use, and you won't have damaged the front side of the badge.
And take pictures!