Can prayer change God's perfect plan?

[Brian37]

I thought the atheist position was that you didn't know if a god exists because there has not been enough proof to convince you of one. Not that you've already concluded that one for sure does not exist. Am I wrong?

It varies. 
Most would call themselves Agnostic Atheists (Don't know for sure, but no evidence of one)
Some are Gnostic Atheists (Know for sure there isn't one).

Most people also vary depending on the god mentioned.  For instance many people on this forums have even stated they outright feel certain saying the God of the Bible does not exist, however that does not mean that no gods exists anywhere.  A lot of the problem comes from the broad and varying definitions of the word God.

I bet you are a Gnostic Atheist about the existence of Zeus, for instance.  But no one actively believes in Zeus anymore, so it isn't a position you need to defend.

Could your personal Abrahamic god exist?  No.  Could a god exist?  Possibly.  <---------------I think this is a common, though not universal, atheist position.

So when you talk about God, it depends on if the atheist is taking it by the broadest definition (any possible god), or the narrower one (the biblical one with all the extra attributes given it by someone personally).

Hope that made some sense.

While it is true you have to ask the individual atheist I don't see the "possibility" and neither do the top scientists the higher up you go in science. Stephen Hawking "A God is not required"<--- For example, and people like Krauss and Greene and so on and so on. 

I see no need to fill in a gap with any type of God/god/s/deity super natural. And again science is currently running away from the idea one is needed to explain everything. 

You cannot take the word "possibility" out of context, it has to be framed with "probability" and or "likelihood". And right now the top scientists are saying that it is so fleetingly unlikely and on top of being unnecessary and superfluous adding more questions it is not worthy of consideration.