Specify the location of custom plug-ins in the options dialog for Visual Assist. See Introduction to Source Links.
Visual Assist build 2223 and older
By default, plug-ins for the Source Links feature of Visual Assist are installed to the default installation directory of Visual Assist. Unfortunately, for all IDEs that support Source Links, that installation directory changes each time you install a build of Visual Assist. If you write a plug-in, you should not install it to the installation directory of Visual Assist.
You can append additional locations of Source Links plug-ins by modifying the following string value in the registry:
HKCU\Software\Whole Tomato\Visual Assist X\<IDE spec>\PluginPaths
Set the value of PluginPaths to a semicolon-delimited list of directories in which Visual Assist should additionally look for plug-ins, then restart Visual Studio to make Visual Assist see the updated path.
Delete the registry entry to restore default behavior.