I am obliged to have my rear fog light on the left side, but it is on the right. I've never fiddled around with my Fiat Punto '94, but I'd like to make the switch myself, if you don't advise against it. Could you provide an outline of switching the side of the rear fog light?
As fog lights are physically different to 'ordinary' ones, you will have to swap bulbs and wires - my assumption is that the reversing light is in the equivalent position on the other side.
If your light housings are transparent, then this is as simple as opening up the housing, swapping the bulbs over and swapping the wires over (either in the boot/trunk or under the dashboard)
Open the boot - remove the little plastic cover near the roof and pull the cloth lining away towards the bottom of the boot. There is 1 nut behind the top one and 1 behind the bottom one. Use a socket set to remove them. Then you can just pull the whole light assembly off. The wires are connected by a clip, so you'll need to pop this off to get the whole light assembly off. Once it is off, just unscrew the 4 or 5 phillips screws to get at the bulbs.
Unfortunately on a 94 Punto the shells are generally tinted, so it won't be as easy. If you swapped the bulbs then the reversing light would end up red, which is probably going to breach driving regulations where you are (in the UK it is illegal) so you need to buy new shells.