and he's in a past that he already knows is not going to result in the future he's familiar with, so it's pretty much fair game with whatever changes he wants to make. Only a matter of how much he wants to muck with things.
Kind of a tough spot, actually. Does he just write down a list of big problems and solutions? (Hey, remember that dictator you froze and shot off into space? Might wanna watch out for him in 4 years or so. Doomsday machine, space ameoba, probe, parasites on Deneva, oh, and these things called the Borg...).
How much does he warn them about in order to save lives, how much does he let slide because it'll, for lack of a better word, build character in the heroes?