Can a Buddhist want to/try to evoke positive change or does that go against Buddhist faith?

By adhering to the practices of right thought, right speech, right action and etc., one necessarily promotes positive change - both in self and other beings. Not only does this assist in the easement of suffering for all, but also produces and continues the chain of positive karma.

The only time this action would be wrong is if the result is positive change for self at the expense of other sentient beings.

This is a very simplified answer, and is my experience and understanding.

Buddhists can want to and try to evoke changes without going against Buddhist ideology. What would depart from Buddhist ideoloy is assuming that that change is positive because it appears to be positive from one viewpoint. For example, the idea of Tibet being free to practice its native Buddhist religion seems to be a positive change, but is it? From the Buddhist practitioning perspective, from the non-Asian perspective, yes. Freedom to be a Buddhist if you like is positive. The Chinese who have an interest in how Tibet is run would find that a negative change.

What Buddhism believes is that change happens and people can influence the direction of change. That's reality and there's nothing wrong with reality. "Positive" however, is a matter of perspective, not reality, and application of perspective as reality is wrong. Does that mean that all change is relative? No. No matter how positive an individuals in a culture may find the use of sex selective abortion, it's not a positive reality because while it helps families to have sons in the short term, it doesn't help the culture if there are few females and many males. Working to enact laws to prevent sex selective abortions can be a positive change in Buddhist paradigm, but only if we realize that not everyone is going to view this positively, for whatever reasons.

The ground floor of Buddhism is abandoning non-virtuous, or destructive, behavior and adopting virtuous, or positive, behavior. That there is impermanence and (karmic) cause and effect is the reason a Buddhist should try and change! Actually, anyone who wants to be happier has to stop doing the things that make them unhappy, Buddhist or not. As you go a little further, you generate certainty that liberation (even enlightenment) is possible - after all, the Buddha was just like us and had suffering and afflictions and so forth but sincerely took concern for others to heart and attained unsurpassable, true complete enlightenment and then began to teach the way to do it to all kinds of beings. In short, because enlightenment is possible, a Buddhist has to purify obscurations and work on themselves. That is the basis of the faith - that change is possible but that it is a result with causes. "May all sentient beings have happiness and the causes of happiness. May all sentient beings be free from suffering and the causes of suffering. May all sentient beings never be separated from the happiness that knows no suffering. May all sentient beings live in equanimity, free from attachment and aversion."

Why wouldn't a buddhist try to evoke positive change, if they didn't, that would go against everything.

Buddhists should always try to make life easier for others. You should never just sit by and do nothing, while a child or other human being suffers.

Buddhism teaches that there is suffering in the world and that there can be an end to suffering. Suffering occurs when the way things are and the way we think they should be do not match. To break this cycle, we must detach oursevles from possession of and to material objects and to all that blocks us on our path towards enlightenment. Buddhism also preaches the philosophy of "be a light unto yourself." And "be the change that you want to see." We always imagine the grass to be greener on the other side when it can be just as green on the side you're on now. What if there is no Heaven and no Hell? What if they are merely metaphors for our earthly action having eternal consequences? If this is the only time you get wouldn't you want to make every day Heaven?

This question is to general for me to try and answer.