The thing is, from many sources I keep hearing that the suggested unchangability of terms and pay is just a negotiation tactic. They will come to you with printed documents, with policies that things totally cannot be changed, it's like that in the system, there is just no way. Then in many cases magically there are suddenly ways to change all those things after some more negotiation. You obviously need a strong position for this, good alternative offers etc, but you don't have to be Michael Jordan for the above story to happen.
A lot more things are open to negotiation than some people imagine. Even including buying a fridge at your local chain store or similar. Not every time, and not to everyone who merely says "I want".