As far as I know, "eveything" is allowed. I know teams using 400V to power a 12V solenoid.
However, in Germany it is not allowed to have a voltage over 48V when working with underaged students.
So we decided to rip of the copper cable of a solenoid and use a 0.5mm wire instead. With this we can kick with 12V and reach the allowed kicking limit. The current of 20A during 20ms is no problem for a LiPo battery.