Looking at http://fallout.wikia.com/wiki/Fallout:_New_Vegas_reputations on the wiki for reputation I was wondering about my stance with the Legion. I was Liked at one point and then did enough bad things to them to become a Soft-Hearted Devil. Is there anyway to become Vilified, or is Soft-Hearted Devil the worst I'll ever be considered? (even if I completly side with the NCR)

If you have already gotten the Mark of Caesar, then no. But Soft-Hearted Devil is the same thing as Villified. If you had a best friend IRL, and kicked his dog over the fence, chances are, even though you did good things for your friend in the past, kicking his dog over the fence probably made him hate you now. Same logic applies to how the faction rep works.

So no matter what bad thing I do to the Legion it can't change to Vilified in name, correct?

Also, at Soft-Hearted Devil will Legion Assassins still come after me? And does being a Soft-Hearted Devil hurt your reputation with the NCR?

Yes and Yes. Minus the recieving the MoC event with Vulpes, there is no way outside of console commands to remove any 'mixed' reputations such as Soft-Hearted Devil. As you basically got it, you are villified in all terms but the word itself.

Thanks for helping me clear that up!