OK, you want to keep the existing motor, I can understand that.
I would recommend then:
Buy a 240V disconnect switch to turn the entire setup off.
use fuses or breakers on both the primary and the secondary of the transformer.
Buy a 240-480V step up transformer
Buy a 480V 3 phase inverter
Keep in mind that you can NEVER change the motor from low speed to high speed while the inverter (VFD) is running. This could destroy the inverter with the inrush. You can operate it at either low or high speed, you just have to stop the inverter first. You cannot have a switch or disconnect between the inverter and the motor.
Also, going from 240 to 480V doesn't necessarily increase the arc flash hazard. Arc flash is a combination of voltage and current. It just so happens that where you find 480V in industry, you also find high arc fault currents. You are using a step UP transformer which actually INCREASES the impedance of the power and might in fact reduce the fault current. Still, whether it's 120 240 or 480, respect it and don't work on it live, and keep all connections enclosed. The drive will most likely have to be in an enclosure because most have exposed terminals.
Final thought, step up transformers are not so common to find. You might use a step down transformer but wire it backwards. This is not universally recommended but can be done for small power levels you are dealing with. This usually causes a good amount of voltage sag (the 480V side) at full load. Luckily though your inverter only needs to make 440V instead of 460V
Brian