Depending on what rule changes you are talking about it doesn't matter if 95% of miners choose to switch to say 50BTC reward forever. The power is with the merchants to reject the false coins.
Please explain to me how they can do that?
They just keep running the code they've been running. It will reject the 'bad' blockchain being produced by 95% of the miners, and accept the 'good' chain being produced by the other 5%.