Lace edging can usually be added to a corset at any time, simply applied over the existing edge binding.
If the lace is very narrow, it should be wrapped around the edge of the corset so it finishes on the inside. Very often, though, the lace is wide enough that it partially covers the grommets or busk hooks of the corset. When that happens, it should not be wrapped around. It needs to be loose against the body of the corset so it will not interfere with the busk or the lacing.
The lace is folded back about 1/2″ underneath itself. Depending upon the particular lace you are using, some sort of an edge finish may be needed for the lace itself to prevent raveling or loose threads. In this case it is simply cut.
The lace is top-stitched to the edge binding after the corset is technically finished. What kind of stitch you want to use depends upon the lace you are using and the look you want. Very often a straight stitch will work nicely. Another excellent options is a basting stitch or hand-basting, which allows for easily changing the lace trim later. Lara of http://www.laracorsets.com informed me that ALL historic corsets had the lace basted or tacked on.
In this case I chose a tight decorative stitch that blended into the lace pattern.
The view of the stitching from the inside. I recommend using a basting stitch, rather than a decorative stitch, so the lace can easily be removed, cleaned, or changed.
If the bound edge of the corset meets the front or back at an angle, the edge of the lace needs to be folded so it will lay in the same direction as the vertical edge of the corset. In this case, the sweetheart shaping on the bust meets the busk at a very wide angle, so the lace must be folded so when the busk is closed the lace will meet edge to edge.
Adjust the angle of the fold by hand before stitching it down. The angle needed in this case is shown below.
Every situation is unique and there is more than one way to achieve a beautiful end, but generally this method works well for applying decorative lace edging to most corsets.