I therefore changed his gun arm by cutting it at the bicep and putting a ball joint and hinge (from a transmetal scourge's leg/arm combo). Then I modified the button on the gun arm shoulder so it makes light and sound on a forward motion of the arm. Once I did this I cut the fins around the shield off (where the flip out sword is) with a saw, sanded it down and glued the halves together. I attached it via rare earth magnets that I glued in a carved recess I made at the bottom of the fingers. I also tightened the spring to the flip out sword as it was... floppy.
Once I finished all that I sprayed the whole figure flat black (Testor's enamel) and dry brushed with steel and some finishing touches of copper. I also painted some gloss red in the eyes and mouth so the lighting effect is more pronounced. I also painted red gloss over some of the wiring and thigh booster. Over all I think this is the best figure I've done thus far.
One last thing. Because of what I did to the arm (adding the hinge in the middle), it no longer connects to the light and sound button when in tank mode. So the missile can still be fired, but no more lights and sound. I just manually push the button with my finger (the button is right behind his head).
Below is the original ROTF Megatron: