Q2+4: First, installing something can always harm your computer (just have a look on XP service Pack 3: It completely prevents some computers to start, even after a patch). Thats the reason why one of the first sentences in every EULA (or like that) is always in the meaning of: You are doing it on your own risk. Just have a look in the ROME-EULA. It stands there. 100%. But don't ask me where, I never read them [In Germany I don't need to, its one of the few really good laws: Its only binding if you can read it easely before you buy it]
If and why it harms one computer, but not the 1000 exactly build same (or why something works fine five month but then not for 3 days) is one of the big mysteries of Computer Science. If you solve it, they possibly create a new Nobel Price for you.
I blame Murphy, that little bastard of a cat.


The download is the easy part. Installing it (and apply patches) can be very complicated, but that depends on the Mod. I had some of the "double click and wait until its finshed" and some of the "unpack this, macke this, delete that, create that there...." type.