You basically got to log into YES and start streaming live, then open developer tools on your browser and poke around until you find the M3U. I don't have the time/energy to do a full tutorial but that should get you close. Keep your expectations REALLY low for this. Whenever YES transitions between a live moment and a commercial (and back again) the stream will hang/freeze. Most of the time if you wait (sometimes as long as a full 2 minute commercial break) it will recover and come back. And then, at some point - for me it was about 2 weeks - the m3u will stop working entirely and you'll need to re-authenticate. The M3U URL is specific to YOU and includes an authorization token based on your account (and is probably geo-IP checked as well). It's a fun experiment but (IMHO) not a practical way to get your Yankees fix.
Yes. That is essentially what happens. Not ideal, and would need to re-do every few weeks or so because the token expires, but it gets the job done. You just need to setup a custom m3u file and place the m3u8 stream into the m3u file, and then add the guide data to Channels through something like RCN or DirecTV for example. Yes, freezing does happen as well, so sometimes the stream does have problems.
Can you explain where you find the M3U?
Now that YES seems to do TVE without the separate YesNetwork login, can it be readded?