Have a look at Grayjay for youtube and other video sites.

If it’s a matroska (mkv) file you can use mktoolnix (use the header editor) to set default tracks.

Can’t they be both? Potato potahto.

It will destroy the Universe if we do that. /s

? is the start of the suffixes, & denotes a change in suffix

Technically speaking they are query parameters not suffixes.

Can you give more details? What apps do you use? Anything worth noting? Thinking about doing this myself as well.