You can move the buckles/straps yourself very easily. The strap that goes through the hole is moved, and the buckle on the opposite side.
What you absolutely MUST do, is make sure that you sew right through the whole kilt from the surface where you are re-attaching through to the lining inside. The interior stitches won't be pretty, but since they're next to your body, nobody will ever see them. If you do not go right through, your kilt will, over time, soon distort the tartan and perhaps even rip out. The tartan is not strong enough to support the pull of the stitches, which is why the kilt is structured with heavy duty linings.
To set it up, the tongue of the buckle ideally goes through the middle hole on the strap to allow for simple, non-intrusive future adjustments.
Other advice on this simple process can be found here on XMarks in several threads, and I would presume that others will add shortly to what I have said here.
I have done this several times, and my tailoring skills are otherwise limited to replacing buttons.
The best news is that if it doesn't turn out just the way you want it, it's easy to reverse the process or adjust further.
Good luck, and let us know how it turns out! 
Rev'd Father Bill White: Mostly retired Parish Priest & former Elementary Headmaster. Lover of God, dogs, most people, joy, tradition, humour & clarity. Legion Padre, theologian, teacher, philosopher, linguist, encourager of hearts & souls & a firm believer in dignity, decency, & duty. A proud Canadian Sinclair.
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