Sure, this would certainly be possible!
The *.bundle formats includes “library.json” inside, which can be generated outside the OpenFL tools.
If you are using OpenFL for your editor, you can import some of our classes to make this more automatic.
var manifest = new AssetManifest ();
//manifest.libraryType = "your.custom.AssetLibraryClass";
//manifest.libraryArgs = ;
File.saveContent ("path/to/library.bundle/library.json", manifest.serialize ());