I ran some calculations and it looks like on flat ground a 24 Mile range may be able to be realized with the 48V 14Ah battery pack, however, the calculation was very close so it may or may not fall a little short of that.
Whether the motor runs too hot when overvolted to 48 Volts depends on how much of a load is applied to the motor and for how long. With some overvolt modifications the motor lasts a long time and with others, the motor burns out very fast.
The Razor EcoSmart scooter controller and wiring harness are a unique design which will not work with most other speed controllers, so you will need to start from scratch on the wiring harness between the batteries and controller, and the power switch will run directly to the new controller instead of being in the wiring harness between the battery pack and controller. If a new battery pack wiring harness is made and the controller's wiring directions are followed then everything should go together very well.