I'm pretty sure that's just a remnant of a 3090 PCB design that was adapted into a 4090 PCB design by the vendor. None of the cards based on the AD102 chip have functional NVLink, not even the expensive A6000 Ada workstation card or the datacenter L40 accelerator, so there's no reason to think NVLink is present on the silicon anymore below the flagship GA100/GH100 chips.
I don't know about this particular scenario, but typically fuses are small wires or resistors that are overloaded so they irreversibly break the connection. Hence the name.
Either done during manufacture or as a one-time programming[1][2].
Though sometimes reprogrammable configuration bits are sometimes also called fuse bits. The Atmega328P of Arduino fame uses flash[3] for its "fuses".
Not at the scale we're talking about here. These structures are very thin, far thinner than bond wires which is about the largest structure size you can handle without a very, very specialized lab. And you'd need to unsolder the chip, de-cap it, hope the fuse wire you're trying to override is at the top layer, and that you can re-cap the chip afterwards and successfully solder it back on again.
This may be workable for a nation state or a billion dollar megacorp, but not for your average hobbyist hacker.
I miss the days when you could do things like connecting the L5 bridges on the surface of the AMD Athlon XP Palomino [0] CPU packaging with a silver trace pen to transform them into fancier SMP multi-socket capable Athlon MPs, e.g. Barton [1].
Some folks even got this working with only a pencil, haha.
Nowadays, silicon designers have found highly effective ways to close off these hacking avenues, with techniques, such as the microscopic, nearly invisible, and as parent post mentions, totally inaccessible e-fuses.
