The store app has to make the registration in this registry key:
And then set the File association\Capabilities in another key, mentioning each file type it can handle. For example Microsoft Edge has the registration here.
If you can post the export of
RegisteredApplications branch, I can make a REG file which adds the
FileAssociations info for that application.
With this done, the application should be normally displayed in the Open with.. dialog, as well as in Default Apps.
Update (May 3 2016):
You can use this REG file to add .CONF file type, using the same association setting for CodeWriter .txt file type.
Windows Registry Editor Version 5.00
Pls note that you need to take ownership of the above registry key, add yourself full Permissions, then merge the REG file. Once done, reverse the Permissions to defaults.
Note: This REG file is valid for the current version (as of this post) of Code Writer. If you have any other version, make the modification in the appropriate key.
The key might have the following naming/numbering convention or similar.