Fenestrated endografts require 6 to 8 weeks for device customization, and off-the-shelf devices are not yet available and may not be of easy access for urgent repair of complex aneurysms. We describe a technique of stent graft modification in a high-risk male patient with two prior open aortic repairs, end ileostomy, and a rapidly enlarging 10-cm supra-graft type IV thoracoabdominal aortic aneurysm. A Z-stent thoracic stent graft was modified on-site using mini-cuff reinforced fenestrations to incorporate the visceral arteries and improve overlap at the side branch attachment sites. After successful repair, the patient was discharged at 4 days without complications and with patent branched stent grafts without endoleak. On-site modifications of endografts may allow urgent endovascular treatment of complex aortic aneurysms in high-risk patients who are not good candidates for open repair or who do not have access to manufactured fenestrated devices.