As flyrod said, installing a stabilizer is not a complex job. With good instruction and basic hand stitching skills anyone should be able to do it.

Notice that I said should.

The daunting and scary part is taking a razor blade to a perfectly good kilt that you paid a good penny for.

The Stabilizer is a small, thin strip of fabric. Usually broadcloth similar to a bed sheet. It is sewn inside the kilt between the two top buckle tabs.

To install a stabilizer would required you to un-stitch the liner, un-stitch most of the hair canvas interfacing, and remove the buckles.

You then stitch the stabilizer in place firmly sewing it to the pleats and insuring that the stabilizer is just long enough to keep the back of the kilt the original size.

You then re-install the hair canvas interfacing, stitching it to the kilt and to the stabilizer.
Then you re-install the buckles by stitching the tabs completely through the kilt, stabilizer and interfacing.

Finally you put the liner back in place.

I just finished exactly the same job on a regimental kilt. Total time involved was more than if you did it from scratch due to the disassembly required. Say 4 - 4.5 hours.

The sewing part is not hard. Understanding what to do and how to do it so the stabilizer and interfacing do what they are supposed to do is not difficult to learn. Barb's book explains it really well.

As I said the scary part is that first step of cutting into your kilt. Not a job for the faint of heart or those who have never torn a garment apart for an alteration.