Changing from double hung to casement windows will alter the character.

Over time, bad alterations can strip most all the historic character from a building and one of the elements that has the most impact on character are windows.  As such, it’s absolutely critical to pay attention to windows.

In The Truth About Windows you will find a discussion of the issues as well as some great examples of what not to do.  If you are contemplating making some window changes this is a good place to start.