The old leader is not immediately affected in any way. All players try to beat the leader's score. Any who fail are removed. Any who succeed stay in. When all players fail to beat a leader, that leader is the winner.
Any player declining a new rule prevents the change.
Whenever you land on the score of another player, you send them back to the score you started at on that turn. On your turn, you get 75 points. This lands you on your opponent at 115, and on arrival, you send that opponent back to 40. The Insurance Point is an interesting little thing. This would be a wimpout.