Not how blockchain works. You're referring to a 51% attack. The number is arbitrary... what happens is as mining power increases your odds of being able to mine multiple blocks in a row increase, you can still pull off this attack with < 50%... All transactions are still valid, the hashes have to match, they can't control the network, they can do things like re-organize the blocks. Theoretically if someone had enough mining power they could send funds to one person, then after that person has received funds and acted on the belief they have the funds, the miner could attempt reorganizing the blockchain and moving that transaction to a later block and a different transaction spending that same balance to an earlier block... at that point the later transaction would become invalidated. Almost everyone operating on bitcoin is aware of this and requires you to wait for multiple confirmations to prevent these kind of attacks. If you are waiting for 12 confirmations for example it's virtually impossible to re-organize blocks that far back, you'd have to have half of the computing power in the world to pull it off. Not cost effective.

Also modern blockchains like ethereum are moving off of proof-of-work and over to proof-of-stake so it's a non-issue