I'm not sure what defaults you mean that are not set? Have you tried just opening the file manager on the device, looking in the music files, tap on the trimmed file? That should bring up the open with walkout songs option. If it does not bring up that option and just opens the file in some other app, then you do have a preference set that you should be able to clear with the settings app like I described in my last response.
As for an add file to the imported announcement list... I suppose I could add that in the future. I will add that to the feature request list.
Since you are combining the song and announcement to one file, have you tried just adding your file as the players song rather than announcement? Since Best mp3 editor adds the trimmed song to the Android music library, you should see the trimmed song in the Android music files.