NeonBible said:
How do I change the ratio without re-encoding/quality loss?
Unfortunately, the project wasn't made ready for playback to TV (not properly letterbox'ed). You must add such a letterbox and then re-encode. As csd79 noted, that shouldn't be much of a quality problem ..
csd79 said:
But I did the MKV with a high bitrate so anyone who wants to alter it or convert it to DVD or whatever can have a good starting point.
If that is not good enough, one could use his raw capture (if available), and his posted Avisynth scripts & resources (page 1), to recreate the project with a TV-friendly letterbox.