In this particular case we weren’t terribly concerned about the risk, because if everything went haywire we could always disable the campaign as a last resort.

Other kinds of changes that bear the kinds of risk you’re suggesting — like a marketing site redesign that could negatively affect revenue—definitely require care and close monitoring. But those concerns shouldn’t chop you off at the knees and prevent you from taking a shot at improvements or new ideas. You just have to be methodical, A/B test if you can, and ultimately trust your gut. Failing to make any changes because of fear can be just as costly as making the wrong changes.