If someone was to change this "one line of code" if definitely would be considered a "hard fork", regardless of consensus from the core devs.
Definition of hard fork is:
So how exactly would the current version of Bitcoin accept the creation of the 21000001st bitcoin?
However, if you did, all your blocks would be ignored by people that use the original client, and more importably, you'd ignore theirs, effectively separating you in a different network with all those who run your modified client.
What guarantees are there that the supply will be limited? The fact that the community has agreed on accepting bitcoin's rules, which dictate how many coins are introduced.
Whats the point of arguing the semantics anyway. It's not gonna happen, FUD or whatever you are doing is a little pathetic.
because watching bitcoin @300 is like watching blue bars of microsoft installs ..