The issue with adding ram is that the location if the rest of the ram is tied in with the processor and gpu in a single chip. Unlike a computer motherboard, the board in our phones doesn't have a DIMM slot to accept more RAM.
As I'm seeing it, you would need to completely replace the SOC, which would require you to write new drivers for all the phone's hardware so that they could understand what the chip is telling them.
Theoretically possible, but practically unrealistic.
As for the other mods, those could possibly be done, but i don't know what all would be entailed I'm doing that.