Streamtuner2 has a configuration file in ~/.config/streamtuner2/settings.json. You can edit it with any text editor. But take care to correctly pair quotes, and don't omit commas between group values.

{
    "auto_save_appstate": true, 
    "auto_save_stations": true, 
    "debug": false, 
    "dir": "/home/mario/.config/streamtuner2", 
    "dnd_format": "xspf", 
    "google_homepage": true, 
    "heuristic_bookmark_update": false, 
    "history": "20", 
    "icon_dir": "/home/mario/.config/streamtuner2/icons", 
    "internetradio_max_pages": "5", 
    "jamendo_count": "1", 
    "load_favicon": true, 
    "max_streams": "500", 
    "nothreads": false, 
    "play": {
        "audio/*": "vlc --one-instance %xspf", 
        "url/http": "opera", 
        "video/*": "vlc --one-instance", 
    }, 
    "playlist_asis": false, 
    "plugin_auto": true, 
    "plugin_dir": "/home/mario/.config/streamtuner2/plugins", 
    "plugins": {
        "bookmarks": true, 
        "configwin": true, 
        "delicast": false, 
        "dev_console": false, 
        "di": true, 
        "dnd": true, 
        "exportcat": false, 
        "favicon": true, 
        "filtermusic": true, 
        "internet_radio": true, 
        "jamendo": true, 
        "modarchive": false, 
        "myoggradio": true, 
        "pluginmanager2": true, 
        "radionet": true, 
        "radionomy": true, 
        "surfmusik": true, 
        "xiph": true, 
        "youtube": true
    }, 
    "pyquery": true, 
    "record": {
        "audio/*": "xfce4-terminal -e streamripper %srv", 
        "video/youtube": "xfce4-terminal -e \"youtube-dl %srv\""
    }, 
    "retain_deleted": false, 
    "reuse_m3u": true, 
    "share": "/home/mario/projects/streamtuner2", 
    "show_bookmarks": true, 
    "show_favicons": true, 
    "tmp": "/tmp/streamtuner2", 
    "useragent": "Streamtuner2", 
    "window_title": true, 
}

There are three JSON groups:

• the plugins: { } list simply lists which channel and feature modules are enabled.
• And record:
• and player: are the audio/recording apps from the config dialog.

All other fields are individual core and plugin options. They're usually sorted alphabetically. Plugin options often have a name prefix which indicate their belonging.

A few options may not be available in the F12 configuration dialog as checkbox, but can be edited here.

You probably only want to edit it manually if there's a startup problem, which neither -D nor -d pluginoff can fix.