I wanted to add a shortcut to open the preferences of the Alfred app.
These preferences are in the form of a file inside the application itself in the Applications folder.
So, using BTT's standard way, when you want to add a file/application to open, it will allow you to select the Alfred app, but it won't allow you to “open package contents” and select files inside the app.
I think a good solution to this would be to let us edit or add the file path, which the app already shows below the configured action, just not editable.
For the time being, I managed to solve it by adding the folder the file was in to Finder's favorites list in the sidebar, so that when BTT asks me to select a file I can navigate to it.