Two things: a repaired 3090 24gb can be sold for 1000+ euro in Germany at least. It's still crazy expensive, so if you have the skills and devices, it can be done with a profit when you buy 3 broken cards and can sell 2 repaired one.
I never reballed any IC, so I would not dare to try it on my card.
Apple didn't design the PowerPC or make custom variances. Motorola and IBM did it. Especially Altivec was added by Motorola, and IBM didn't like to add it to their PowerPC CPUs when Apple asked for help, when Motorola had the 500 MHz glitch bug back in the day.
I never reballed any IC, so I would not dare to try it on my card.