Forkability of bitcoin-qt?

This is only a question in regards of protecting bitcoin as a whole. Bitcoin is only decentralized to a point. That is the spread of the wallets that can verify the bitcoin blockchain. But the wallet creators are centralized. So in a worst case szenario where the creators of the main bitcoin wallets are forced to do something against bitcoin, that would hurt the network and the wallet-creators couldnt speak about since the law (for example USA) forbids to speak about... how to fight against?

I think if that happens thousands of people will download the newest wallet. Without knowing of the downside. At one point someone will notice... what to do? A fork probably, that will redo the bad changes. But is it doable?

Wouldnt it be best that users then get told something like "Set in your wallet that a fork is started with settings xyz starting from block a."

Couldnt this help as a backup plan against such attacks? Only asking since a way to fight the centralized and so vulnerable aspects of bitcoins would be a good idea i think. But im not sure if that would be a good way.