Question:
Do fighters get to immediately negotiate a new contract if they win the title during the course of their current contracts?
For instance in the cases of Chris Weidman and Anthony Pettis. They both won championships during the course of their current contracts. Now that they are division champs, did they get to renegotiate to championship pay? Which is considerably much more lucrative. 
They automatically get the champion extension I think.
And yes I am sure they throw them a little coin to keep them happy ala bones jones bentley.
It depends what the contract lists. There are general contracts for new fighters but when u get to the champion-status, there are PAGES worth of clauses.
Yea I figured they have to get a nice bump for winning the championship. I was just curious what some of the bump ups were. Was hoping someone here knows.
I'm sure pettis got a nice bump. Dana has to love having a charismatic, exciting fighter who looks to finish his opponents as champ.
Depends how far into their contract they are. Weidman won on his last fight. Lots of negotiation power there. 
Sometimes. Weidman got a new contract (but he had no more fights left). Condit got a new contract after winning an interim title, etc... Bendo got a new contract after beating Nate (so after he defended the title twice). Jones I believe got a new deal after he beat rampage.
Typically, Zuffa pits you up against the styles that would give you the most trouble before new contract talks begin because they want to better determine your actual value.
They use bonuses so they dont have to always be renegotiating a contract.
The Sultan -Question:
Do fighters get to immediately negotiate a new contract if they win the title during the course of their current contracts?
For instance in the cases of Chris Weidman and Anthony Pettis. They both won championships during the course of their current contracts. Now that they are division champs, did they get to renegotiate to championship pay? Which is considerably much more lucrative.
It Varies, but alot of guys that are about to fight for the belt are offered to negotiate the terms of their new champ contract in case become champs. Wiedman had a chance to do that but refused, he wanted to wait until he was champ so he could negotiate from a better position as the actual champ and not the possible champ.