Bought a used UK Mocker from KiltedTaper a while back. While I love it and have worn it a few times, it was a little long and just a bit too big in the waist. Here's what I did.

I took off the belt loops (all of them). Sewed a small dart right in the back center seam that took about 1 inch off the waist. I sewed it from the same place where the pleats are sewn down (fell?) up to the waist.

Before I sewed the waist band down on the inside, I cut away some of the material that I created with the dart (reduced the bulk a bit).

Then I turned the entire waist band under from the outside to the inside. If you have a UK, hold the waist band in your hand and fold it over. You will feel where the bulk of the material is under there.

Then I sewed it down by hand on the inside. If you decide to do this, take care on the upper apron to make sure your stitches don't go all the way through. True your belt is going to cover it but . . .

When that was done: the waist band on the front is now only about 3/4 of an inch wide - it looks good, actually consistant with front pockets and the tops of the back pockets.

Finally, I sewed the belt loops back on (most of them) with the sewing machine. I think they are a bit smaller now than they were before I started but they still work fine for me.

When I tried it on, it fit perfectly!! The length was just right, the waist is now snug and the way it hangs and sways is even better than before.

All this to say that even though it wasn't a proper way to alter a kilt, this time it worked out fine.