That's not how Bitcoin works at all. No amount of the supply (or hashpower) can let you make arbitrary decisions.
Having 50+% of the hashpower could let you double spend by mining on two forks in parallel, but it will never let you change the rules of the protocol, since these are defined on clients run by many people.
In fact that is what happened in the article. Someone realized there was a problem, got everyone to change their clients, and it changed. The first person to notice the bug did not need to hold any Bitcoin at all to make this change.
Right but some number of humans can collectively decided to change literally anything about Bitcoin. It isn't some fundamental constant of nature. The question really is who are the humans that could actually decide this, what are their incentives, what would make them decide to change it? If only you and I are running the original Bitcoin code then it isn't really Bitcoin. "Real" Bitcoin is a function of human decisions and has fundamentally very little to do with the code. Purchasing Bitcoin is simply a decision to trust this group of humans.
Yes, but who actually decides? I doubt it is as egalitarian as it seems. Perhaps to put it in monetary terms, how much money would be required to incentivize this group to double the number of Bitcoin? Would $999T be sufficient?
If anyone creates a different bitcoin version with double the number of bitcoins, that new network would be worthless.
Not only would no-one have confidence that the same thing wouldnt happen again, but the value of the bitcoin in this new version would be half that of the old system. No one who holds bitcoin (the people who count here) would agree to use the new version. It would be dead in the water.
Even if it did manage to gain traction (which it wouldn't), the people still using the old version would prevail due to their use of harder money, just as bitcoiners are prevailing over fiat-holders.
It's like trying to change the text of the bible - something of that order of difficulty but still much, much harder due to the enormous incentives to carry on using the previous harder version.
Having 50+% of the hashpower could let you double spend by mining on two forks in parallel, but it will never let you change the rules of the protocol, since these are defined on clients run by many people.
In fact that is what happened in the article. Someone realized there was a problem, got everyone to change their clients, and it changed. The first person to notice the bug did not need to hold any Bitcoin at all to make this change.