Pretty much... If you copy them and then modify them you are still copying them, which is something (we assume) you don't have the right to do. However ToS aren't that hard to just write and there probably wouldn't be that much difference between the time needed to copy and modify than to just write them. Hope that helps
As above, it would be, but depending on how much you have changed them it may be difficult to prove that you originally copied them as T&Cs tend to be very similar on similar sites.