Yes overvolting can either blow your controller or work very well. I did an overvolt on a 24volt controller up to 36 volts and is still working, then again I did an overvolt on a 36 volt controller that worked fine too until I draged the solder wick across the circuit board. The only thing you cant overvolt is your batteries. They must be charged to or very close to the manufactures specs or else you will kill them very fast.
If you overvolt your controller and hub you may or will lose your waranty on all and any items that maybe damaged by being connected to your mod, including your batteries and hub...
Dont do it unless you are into learning a lot more about the controllers, their components, proper soldering techniques and purchasing the gear you need to remove components and replace components from and back onto the printed circuit boards. Removing 12 fets is like pulling your teeth out and expecting them to go in again without an issue. It is a big job even for a pro tech.
Lesson's I've learnt modding controllers.
If its not broken don't fix it.
If its easy then you probably get away with it.
If you work a mod and it works don't mess with it..
Some overvolts can take away the efficiency away from the controller, you may have to tweak the other surrounding components to regain effieciency, now this is all fine and well but the stuff that happen to a pcb while tinkering can set you back a few steps. One needs to have a comprehensive knowledge of the power regulators on the board, You cant just replace caps and fets. Resistors, zeners and voltage regs do all of the important work in regulating the voltage not fets.
Many fets can take a source voltage over the factory rating and output for many years providing they are well heat sinked, in fact many fets already on controllers are already capable of taking the source voltage well over 36 (43) volts, but give them to much gate voltage like 8 volts more than they should and you'll blow em up fast...
I am lucky atm I have cheap resource of factory second controllers to play with but I would not do it to the expensive ones nor would I put a $1800 lifepo4 pack at risk playing with controller mods. One thing goes wrong and you can melt everything.
overvolt = risk
You have to wear "all" the damages if you want to get your hands dirty.