Mid pipes (X-Pipe, H-Pipe, or Y-Pipe) come in two main varieties, those with and those without catalytic converters.
For mid-pipes that come with catalytic converters, a new or updated tune is not required, but is recommended.
For mid-pipes without catalytic converters (off-road), a new or updated tune is required.
This is because the elimination of the catalytic converters removes what was a large portion of constricted airway for your exhaust system. A new or updated tune can allow you to take advantage of the maximum potential that this change offers, while keeping those Check Engine Lights at bay! These pesky lights can result in emissions test failures in applicable states & locales.
**Be sure to check with your local authorities to verify what is & is not legal in your area.