Throw me the Idol, I'll Throw you the Whip

So at my current job, I'm working on a quite profitable big website that has been written in Java with javascript and velocity templates and css and html continuously for the last seven years. Given that I'm relatively pleased with the state of the codebase. It's not totally nuts, and while I don't agree with the code formatting conventions they're mostly followed.

However it's huge and has a large number of interlocking parts and it's making money all the time so don't break it. That said, there is nothing really preventing me from breaking it beyond some automated tests and my desire not to. And the corollary to it's making money all the time is that's because we're making it better all the time, so there's always a change to go in.

The whole thing is a lot like archaeology - not real archaeology, but Indiana Jones archaeology where you have to figure out how to get the idol out of the deadly trap or perhaps ancient weather control machine or maybe it's an alien time capsule, without setting off the thing and causing the end of the movie.