It can be done but, it has it's pitfalls
The v-glide and resistor coils are engineered for 36v worth of heat. More voltage will increase the heat and can result in a melt down of either or both of the units......
Now, having said that ..... I have run the stock cart on 48v for a year by simply driving WOT or nothing; minimizing the amount of time I put the juice thru the resistors. If you run wide open throttle the resistors are out of the circuit all together... hope this helps.