I am not an airplane engineer. Part of the certification is that you can do this. Elongating the body would be a different thing again. My "new certification"

I am not an airplane engineer. Part of the certification is that you can do this. Elongating the body would be a different thing again. My "new certification" was in regarding to the Federal Aviation Administration. You are referring to pilots certification. Yes, after the FAA gives green light, the plane is certified. And a pilot may or may not, based in his types of licenses fly the plane or require new training. In case of 737-Max new training was not deemed necessary. :-(