Their changes? They aren't coders!Actually I think they can mess up BTC but only if people running bitcoin-qt(miners) accept their changes. Miners are the ones controlling what version of the bitcoin software is accepted.. so the question is why wouldn't they eventually go corrupt (like every one else) and make a version of BTC that gives them more BTC/rewards for mining?
The foundation is just another parasitical class of people trying to grab power when they don't have any inherently. In the end there is no avoiding the fact that they don't have any actual power over the bitcoin protocol nor mining community. Being all cozy with the regulators is going to put them in a very dubious position one day when the regulators expect things from them and they can't deliver.