Absolutely it can be modified. I had a E-flite Six Series In-runner in mine, I had to limit it to about 60% power though as that is all the airframe could handle. I have seen others that mount 480 Brush-less Outrunners also, either way its about 20x more powerfull than stock and will go verticle till its out of sight. A 1300 3S Lipo should fit in the stock battery box or a 2200 3S will fit inside the fuselage.

You can also add ailerons/flaperons and flatten the wing which will take the self correctivness out of the plane and make it fly like a "real" plane. This would be a good next step as it is then a true 4 channel plane and will fly like one.