in response to OP:
modding is legal, they finally updated their ToS.
in order for a mod developer to sue you (USC title 17) they would first have to register their work with the copyright office. Which they can under sec. 106a, but then mojang would have to get involved to determine the legal status of the mod, and most courts would just throw out the case as the mod developer wouldn't be able to prove financial damages so they would have to prove damage the honor or reputation. In the case of running a Tekkit server, they cannot.
Modpacks are perfectly legal under USC title 17 sec. 109 "Fair Use"
fun fact: BTW is illegal under SCR 336 (i think it's 336. I'm not super familiar with canadian copyright law).
Finally, just use it. You're not important. Even if there is a DMCA takedown request, you could easily get it reversed and the aforementioned are some good arguments to make that happen.