Various embodiments of the present disclosure are directed to a gaming system and method providing a slot game including a symbol generator modification event. In various embodiments, the gaming system is configured to provide a slot game, each play of which employs a subset of a plurality of symbol generators. If a symbol generator modification event occurs in association with a first play that employs a first subset of the symbol generators, the gaming system removes one of the symbol generators from the first subset and adds another one of the plurality of symbol generators to the first subset to form a second subset, and employs the second subset for a second play. The gaming system removes and adds the symbol generators to form the second subset such that the average expected payback percentage of the second play is greater than the average expected payback percentage of the first play.