hmm, I was under the impression that along with most other mobile parts CPUs were permanently attached to the motherboard by solder.
I'll look into it for you, though I doubt it can be done conventionally through swapping parts. I just have a few questions.
What is the exact brand and model of your laptop?
How will you manage to purchase the a8? I haven't seen any mobile CPU's on the market other than the i5 2420m
Yes you can. FS1 is the mobile socket and it's exactly that, a socket. You can put any FS1 CPU into that socket and it'll work.
Now for the warning that goes with the above. Mobile laptops are designed with a very tight power / heat envelope, putting a CPU that the laptop was not designed for into it could cause heat issues and possibly instability from it drawing too much power.
Also locked memory bus speeds might become an issue depending on the CPU you have and what your trying to put inside.
While a more powerful Llano APU can fit into the socket, the BIOS may not be able to recognize it. If the BIOS cannot identify the APU (or CPU), then the laptop may not even be useable or it works, but the APU is running at a lower speed.
The manufacture may or may not have a BIOS update that will allow you to install a more powerful APU. Chances are there will not be a BIOS update that allows you to do so. Why? See palladin9479's reply above.