As the kilt will need to be lengthened perhaps two or three times, I would not press the edge.

Try turning the hem up by hand - select a fine horisontal stripe at the right height and a matching thread. Now make three stitches in the edge, one which is like this ( - )and two to make an X over the top of it. You don't need to put a knot in the end. Now put a small stitch into the stripe and then put the needle through the edge once, small stitch in the stripe and then go through the edge. Don't pull too tight. You can easily avoid putting stitches in the lighter coloured vertical stripes, and it makes a neat job.

Now look at the new lower edge. It needs to look neat, but if you press it into a sharp crease it might show when let down, so pick a colour that matches or is just a little darker (lighter threads show far more than dark) and sew along the inside of the hem, fairly close to the lower edge so it is held in a tight fold. You can fold the pleats and 'oversew' the two edges maybe 1/8th of an inch from the fold, sew through a nice lot of threads for the stitches to hold and there won't be pulling - or at least not as much as sewing through a few threads on the edge.

If you sew from the back and have the needle more or less flat to the fabric you can make a stitch which is fairly easy to see from the back, but which just surfaces on the outside of the kilt. You can do two or three stitches at a time if you have a fairly long needle - I tell people 'think of the Lock Ness Monster and you'll get the idea'.

Unpicking is fairly easy as you can use a seam ripper to cut through the stitches holding the pleats and then ease the threads out from the back using the eye end of a strong needle. If there are marks left, pat them with a damp sponge or cloth and work the cloth gently - hold it left and right of a small area and twist it gently on the diagonals first one way then the other so the threads move over eachother and hopefully move back into place.

You might need to press the pleats. Do that before putting in another hem - you want to keep the kilt so it will look right when returned to un hemmed condition, so always press in what you want to keep, not the temporary hem.