Have recently have created an extension to import/export VBA code from a Visio drawing or stencil. You can find this useful if you want to track VBA source code changes in your Visio files, like compare current version of the code with the past version. Could make sense to use together with some version control like TFS, Subversion, or GIT.
VBA Import/Export for Visio
Basically the code was inspired by the nice article on excel and CodeCleaner. Unfortunately the code in that article is in a form of a VBA macro, which may sometimes be not that handy (you'll need to copy that over and over to every document where you want to use it), and right out of the box that code does not work for Visio. So this extension addresses these issues (you get the code import/export with one click), also it allows you to export code in "ThisDocument", and supports x64 version of Visio.
The source code of the extension is available on the github: