Chosen Solution

Can I replace my APU or the CPU also the Southbridge chip can that be replaced with the new one or are they connected to the motherboard “married”?

I don’t think anyone has tried this AFAIK because there is really no incentive in doing so when weighed against buying another console second hand or new. The tools, experience and time to get or have this done would far outweigh the above. The chips you’ve mentioned are most likely all be married by each other.