I think Owlus beat me to most of my point (xD), but I'll elaborate on what she said.
While your theory in its present state is a good idea, and I wish we could just follow through with it, there's a main factor here that isn't quite right, that actually is preventing us from carrying out this action.
That being, a source code is not something found in the game itself. If it were, Razmirz could just pluck it out himself and we'd all be happy with brand new updates whenever we wanted.
But, it unfortunately doesn't work that way. The source codes are what allows the game creator/head administrator to go into the game's encrypted codes and change them, as if changing the very framework of the game itself, the way no texture mod or additional emote could ever do. It's like adding on a second tail to your lion, so to speak (sorry for the weird metaphor).
FH+ was added during the time when KovuLKD was still here with us, and so he approved Simba's additions to the game, and once Simba had finished the work, Kov used his source codes to add FH+ into the encrypted files, himself. So, Simba never really "found" the source codes, per se.
But, as you mentioned with the current game mods that are being released by users all the time, we could theoretically update the game that way. However, without those source codes, we can't make everybody see the "go update FH!" pop-up appear when they try to log in and play, therefore it wouldn't be very efficient. People would be playing two different games, even-- and that would be chaotic and confusing, especially to members who come back after a long time and suddenly hear users talking about new stuff they've never even heard of.
We've thought of that, too, but it's just so inefficient that it may be more trouble than it's worth. Not to mention the gray area of legality in changing the game, since it is Kov's creation, despite him throwing his staff and his growing community out to the wind like he has for the past year.
So, you do have a good idea, but there's more to it than some codes found in the dark corners of your FH folder. I wish it could be that easy, though. ;P