The tour's chief says that players who have joined the league will not be welcome back.
The average purse of the 12 PGA events will be $20 million.
The top players will play in all the events.
The changes came after a meeting between Tiger Woods and other top players.
A number of high-profile players have left the established tours for the new Saudi-backed eight- event series.
The PGA banned many of them, including major winners, after they joined.
If the changes to the PGA Tour lure them back, they won't be welcomed back, according to the man. They made a commitment to join the golf series.
Most of them have made multi- year commitments. Every player has a choice, and I respect their choice, but they have made it. We've got ours.
The reigning Open and Players Championship winner is said to be joining LIV Golf, and according to the golfer, he spoke to the Australian.
"I don't care if they leave or not, it's not going to make a difference to me, but I would at least like people to make a decision that is completely informed."
Speaking before the Tour Championship - the final PGA Tour event of the season - Monahan explained that the top players would play in all four majors, the Players Championship, 12 events with increased prize money, and an additional three events per season
The player impact programme has been changed to pay players who generate coverage for the tour.
The reward will be doubled from $50 million to $100 million.
There will be guaranteed earnings of at least $500,000 for every player who is in the priority category of the tour.
The man was asked if making the changes earlier could have stopped the start up of LIV Golf.
He said there was no scenario where they weren't launching.
We are going to make more of the moves that we are making right now.