"90mm dia and only weighs 1kg. "

Sounds like it might even fit in the case and be done with it.

Then of course you halve the fuse rating, it goes right where the cord comes in, not AFTER what you add to the unit. In fact it should go after the switch as well and go off when you shut it off. Why keep bothering electrons needlessly ? So you are merely interrupting the wires going to the original power transformer primary. That way, you also don't have to **** with the casps across the switches and any of that. If it has those buck wound noise filters you might have a slight problem but I doubt it. gonna change 1 kV caps to 2 kV ? No reason to I think. If anyone does, say so, I am all ears. but t here sahouldn't be more than 1 kV on a 220 line either.

And then you put a sticker on it to that effect, the lower fuse rating included.

Actually, half might be too low because of inefficiency and cause nuisances.. If it was three amps use a two. If it is less than two amps, just don't really worry about it. If you must, put another fuse of the original value after the output of your transformer. But anyting less than an amp is already so safe you don't need to go farther. Ground faults are a different subject, but you don't seem to have that problem, right ?