Bitcoin is also a "protocol" - an agreement between devices. If you use the Bitcoin protocol, the rules are that only 21M BTC will be generated, no exceptions. If someone decided that there should be 40 million BTC, it would be rejected by the network, as it is not part of the Bitcoin protocol.
Still, one could attempt to create an alternate currency similar to Bitcoin with 40 million units, but those coins would be incompatible with the Bitcoin network. For the new protocol to succeed, it would have to attract users, and essentially replace BTC in popular support. Highly, highly unlikely. And if it were to become reality, it would be because users chose the alternate currency, not because of a nefarious entity.
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