I am told for some hospital equipment you can get a plug without a fuse, where failure of equipment could cause death, however it seems wrong to me, as you would still have RCD and MCB protection to the supply so it still could fail, so I suppose it is because the equipment uses more than 13A and they want to be able to use it in the home, however since 13A sockets could be supplied with a 16A supply from a MCB which would likely trip before any 13A fuse would blow it still seems flawed to me.
However what is shown is clearly just a photo opportunity as you could not replace the cover. I have seen vehicles with rods replacing fuses put there by the manufacturer. It was in a Lucas 2TU trailer towing unit, these 1970's devices had relays for brake light and indicators when Austin brought out a system where the brake lights were dimmed at night so to reduce dazzle, the 2TU did not load the vehicles own lighting system so bulb monitoring still worked. However in the vehicle in question it was located in a hard to reach place so the fuse was put where there was easy access, and the built in fuse holder of the 2TU had a metal bar to bridge contacts.
However with trailers it was possible for a trailer fault to cause a fuse to blow and so the driver may report and then want to use a different trailer, I can't see where a fuse would blow and you would not need assess to the plug and socket to under take replacement or repair, so I can't see why the 13A fuse would ever need replacing with a metal bar. I have seen many times where a fuse could physical be fitted that a shorting link is used correctly instead. Normally for a neutral, but can't see any reason for using a link instead of a 13A fuse.
Be it a welding set or medical equipment, if it needs more than 13A then don't use a 13A socket, simple.