As far as I know it is not, what makes you think so?
Of course the game is based on Quake 3 engine, and the source for that was released a while ago. But that should not include any changes the Medal of Honor devs made.

I ask because I wanted to change it so I didn't have to reload my weapon; it's a stupid "feature" that has made its way into too many first person shooters. If I want to fuck around reloading a gun while being shot at I'll join the friggin army.

There is the openmohaa project, which used ioquake3 source code to recreate allied assault. It's considered a dead project though.