The corset is what supports the dress. If you lower the back, you will take away the support. I don't recommend this, especially if the dress is strapless..
you fall in love with a dress for everything that it comes with. when you start to want to alter things from a dress and change the way it looks you then should continue to look for your perfect dress
usualy corsets cant be altered that much unless you want to raise up the dress a little bit like i had done.
when is your wedding can you afford to scrap the dress and look for something with a lower back?
it sounds like you are not in love with the back of the dress
A great tailor can do almost anything, but it comes with a price. The bigger the alteration, the bigger the price. Something big can run hundreds of dollars--this isn't $40 to hem a simple column dress.
Also, consider whether the corset back, in your size, is large enough for a zipper. If you go this route, you may have to choose a larger size so there is enough fabric to go across your back for the two sides of the zipper to meet. Or, if you have the dress, you may have to select fabric to create panels.
Re: Can you alter a corset style dress to have a lower back?