I’m aware that Mi Yodeya has its own Nusach. All I see of it, though, is a special Al Hanissim and other changes on 19 Shevat. Are there any other liturgical changes compared to the more standard nusachos? Where can I find a copy of this Siddur?
There's no question that you want to get Siddur Yechaveh Da'at available at just about any Jewish bookstore.
Mi Yodya is a site with both questions and answers. It's a knowledge site. But, frequently, I'm sure you've wondered how moderators decide what are appropriate questions, how things should be tagged, when questions should be closed by the moderators, and when some moderators should interject some remarks. There are a lot of rules. Where do they get this knowledge from, and how can you become as smart as they in knowing all these rules?
Well, you'll find the answers in the siddur that is, indeed, true to it's name. Yechave Da'at means "Tell knowledge" (See Tehillim (Psalms) 19:3.)