By creating the fork on demand. The only part of Bitcoin that is technically hard to recreate from scratch is the huge hashing power of its mining network.

If buyers were happy with bitcoin-but-a-different-brand then there isn't much existing bitcoin holders can do to hold their market together. There is an unlimited supply of numbers out there, the constraint is numbers that are backed by whatever silly number of hashes per second the Bitcoin network is up to. The holders don't have any particular influence over that constraint.