That's not the problem. The problem here is that Fuji appears to be claiming that
any use of the SDK voids the warranty
entirely, regardless of the defect. t would be like if you swapped out your car's engine with a more powerful one, and then, from a completely unrelated fault, its navigation system stops working.
In the US, my understanding is that this is explicitly not legal, per the Magnuson–Moss Warranty Act. FujiFilm can choose not to offer a warranty at all, but if they offer one, then it must cover defects on modified devices unless they can show that the modification caused or contributed to the defect.
In the EU, it is my understanding that it is legal to have a guarantee with terms like these. However, regardless of any guarantee the manufacturer may offer, there is a statutory guarantee in the EU for most products, which completely ignores the terms that the manufacturer might prefer. This usually ends up being weaker than Magnuson–Moss in terms of duration and modifications. But it usually means that for six months, the seller must prove that the fault with the product was caused by the consumer, and for two years, if you can show that the problem is from a defect with the device originally and not from you, then you can still get repairs, replacement, or a refund.