: If in your mod you portray the Friedens and the Koslovics as having
: originated from sassy 22nd-century hipster baristas that were violently
: arguing about Nickelback's role in music history, I really don't think
: you'd hear any knocks on your door from MS Legal -- my (considerably
: double-checked) understanding is that what matters is whether or not
: you're using the Halo IP for monetary purposes. How far off the beaten
: lore path you go with your content really isn't kept track of (the only
: possible exceptions I can think of to this would be if you did anything
: pornographic or similarly shocking with the Halo IP).

Even that won't get them riled up, there's tons of Halo rule 34 out there and I've never heard of them going after anyone for it. The thing to watch out for would be defamation. I don't know how you could defame an intellectual property, but I'm pretty sure you could. You could definitely defame Microsoft, although it would have be pretty serious to stand out from what people say about them on a day-to-day basis. So in my thoroughly inexpert opinion as long as you don't make any money and MS doesn't decide they just don't like the project existing, you're in the clear.
Now, how can we combine Halo, Big Bird, Carmen Sandiego, and Nickelback....