All 31 buyyers were not agree but you reduced it. You said if ALL ! And the reduce is a lot more than 66% !
On other way, you gave 1600 sat/h which compensate the invest of buyers, thank you for that.
But as you said that you will pay the looses from your pocket and change it only if all buyers are agree, Ithink you should only change the upgrades from people who accepted the new deal and let the others play as it was.

In all the cases, you did a good job with your game and I wish you good luck with it !

One more question. As upgrades are cumulative, How will it works if a player buy 10 upgrades at the same time ? You will have to pay him 10 times more, but he will not generate more ad revenu. It could put you in red !