Running a majority of the nodes does not give you the ability to arbitrarily decide to accept an alternate history. One of the big value adds of bitcoin is that

Running a majority of the nodes does not give you the ability to arbitrarily decide to accept an alternate history. One of the big value adds of bitcoin is that every node can decide on its own, without consulting other nodes, whether a transaction is valid or not. There is absolutely a thermodynamic cost to reversing a transaction in bitcoin. Having the miners run an alternate client doesn't change that.