Almost any wedding dress can be converted from a zipper back to a corset back. The hardest part is matching fabric. Most seamstresses that work through a bridal shop or have connections with a bridal shop can get them to order a corset kit from the manufacturer of the dress so the fabric matches perfectly (We do this at Alterations By Christy).
There are uaually two reasons that someone would want to do this. The most common reason is that the dress is too small and won’t zip up past the waist. For a dress to be converted to a corset back, it MUST fit in the hip area.! If the dress is too tight and won’t go down over the hips or buckles at the waist, than it won’t work.
The second reason is that you just like the corset style dress, even though the dress is a perfect fit. If this is the case, than you will have to have the dress taken up in the sides to make it too small to zip, creating a gap of space for the corset.
The cost to do this is usually around $100.00, so be sure you factor that in when making a buying decision.