Actually, don't wanna sound super pseudo intellectual but you can make a fighter have a second engine easily. You don't have to redesign the entire fighter, just add another engine. One of the reasons why the double engine F-35 program was even considered was because it would be the cheapest way to make a twin engine multirole fighter. Why? Because airframe design is quite easy, rather than designing a new fighter. You can easily can airframe characteristics to have another engine with elongation/widening of the body. This was told by Lockheed Martin as means to upgrade the fighter. Though for the JF-17 it is quite meh. I mean for that we would need to design a new radar cuz the KJ-7A is shit for the body we use, not to mention new sensors and data to make the cost more reasonable. The best we could do is get some J-15 or J-16 radar, while using China's help to design the electronic suite of the jet ourselves. Which is possible and easier, had we designed the JF-17 alone. So yeah, stupid idea but in the realms of possibility. Though the chances are below 1% cuz the JF-17 was not supposed to do any of these roles. I mean it's still good enough to carry enough ordinance and good enough range to defend against immediate threats. It was not designed for extended strikes nor was it design to carry heavy payloads.