not sure what lapping means but.
there are 2 options where you wont/slightly damage your cpu when taking it apart from the heatsink.
what you do is stick it back into the mobo, turn it on, and wait for about 10 minute where the cpu wouldve gotten hot, and the thermal paste wouldve gotten soft, then take it apart slowely.
second option is to heat up the heatsink with a lighter or some sort, and heat it till it becomes easier to take it apart.
i wouldnt suggest you doing it if you have no idea what you are doing.
not sure if these are the right thing to say though....