It might be doable IF you have €30,000 to €40,000 to spare for the necessary equipment to do the physical work as well as a couple of dozen PEs to play with. That assumes the replacement CPU is pin compatible and signal level compatible as well.
You will need the 24 - or more - PEs because as soon as you manage to get a new CPU installed you will discover what else you will have to replace because that component, or components, will die - some not very gracefully, so you start again. You repeat this procedure until you eventually end up with - maybe - a working unit.
Basically what I'm saying is you would be better off spending that amount of money on getting a specialist company in the far east to design and build you a new motherboard. Then you will most probably need a new case, larger battery and so on.