Actually, with fuses it's the exact opposite...
You can go lower, not higher.
Amperage is resistance in the line... My ballast runs on 5.5 amps, but when you turn it on it spikes around 6.2 amps...
The fuse has a limit of 10 amps, so, if the ballast tries to pull more than 10 amps the fuse blows...
A fuse limits the amount of amps that a device can draw...
If you need to limit it to 5 amps, you could try to use a 4 amp fuse, but most likely the 4 amp fuse will blow, and it wont work.
If you went higher, like putting a 6 amp in place of a 5, it will allow the device to pull up to 6 amps, and that might be enough to blow it up...
That's why I figured using a 125v would be safe to try, having the correct amperage and all... and I still don't know what's up with the ballast, it's surely broken, it popped and made the electric smoke smell...
I'm going to look into it further, less send the ballast back to be remanufactured.