It may be, it would be best to remove the heatsink but if you need to put too much force in don't bother - at least then you know what heatsink to use with the CPU! You can always take the CPU off without the Heatsink off first. Not too good though; always try to get it off.
the Heatsink and the CPU are pretty strong and metal - just stick a nice small screwdriver between them and lever one off the other. When you put it back on you should still put on some new Heatsink Glue just incase though.