Can I change the handlebar width or stem length on an aero bike with an integrated cockpit?

It depends on the specific system. Most integrated cockpits use a two-piece design where the stem attaches to a proprietary bar, allowing stem length changes within the manufacturer's range. Some use a one-piece bar/stem that cannot be adjusted. Always check the specific system's options before purchasing, and confirm that your ideal fit dimensions are available. Proprietary replacement parts are typically more expensive and may have limited availability.