In my OpenExchange plugin, I am targeting versions 2011 through 2015 of Trados Studio, but using the same code for all three. To avoid having to have three separate Visual Studio projects or to have to manually point to the correct references and target the correct .NET framework version, I've come up with some custom MSBuild tasks to allow me to do this automatically, simply by selecting custom build configurations from the drop-down in Visual Studio. In case anyone is interested in doing this, I've written n article to describe the process here.