Visual Studio 2013 support has been added March 21, 2014.
UIMap Toolbox allows you to restructure, split and merge UIMaps created for Microsoft CodedUI tests in Visual Studio 2010, 2012 and 2013. Developed in C#/.NET 4.0
User Guide including some thoughts on developing maintainable CodedUI tests can be found on the Documentation page.
Integrates into Visual Studio, so it's possible to open UIMap Toolbox directly from the Solution Explorer window:
UIMap Toolbox with two UIMaps opened: