In the description, it mentions that the Y-pipe will require custom tuning in order to avoid engine damage and avoid CELs. Can you explain why this alone without tuning cause engine damage?
Downpipes (even catted downpipes) flow enough air and reduce back pressure enough that they lean our your truck's Air/Fuel Ratio by at least some extent, and could cause a lean condition in your engine under the right circumstances. Tuning is required to increase fuel rates and adjust fuel curves to prevent that, while also disabling the rearward oxygen sensors to prevent a CEL.