Is it possible that an attacker would edit the bitcoin software by only changing the genesis block and rebranding the coin (changing the software name, coin name, etc), and be able to use this new coin with the same bitcoin network meaning his coin would have the same security? Imagine this modified software would consider valid only the coins that belong to the genesis branch. The rest of the UTXOs would have value 0. How could bitcoin miners and bitcoin users protect themselves from such an attack? This is pure speculation obviously, and this also considers that this "new" client would generate interest in new people, institutions, etc.