Build a launch file to launch files of certain types along with directories in certain applications skipping the system file associations.
Shows an open with menu when it detects you have more than one type of an extension in the launch file configuration.
You can also create application listings with specific command line arguments to do certain things for you when launching the file.
Choose where directories will get opened with a special variable in each of the Application Extensions that support folders. See below for note and example.
Even more not listed in this brief list.
You should create an application entry just for directories for windows explorer, so that you may still open directories with windows explorer if you have at least one application that supports directories. See "Example #1" for what a entry for that might look like.