Quoted from DefaultGen:Wow, replacing magnet cores is harder than I expected! Only through a combination of the rawest brute strength, a big new screwdriver, pliers, and my anvil happening to have a hole/edge perfectly shaped for the task was I able to break both free. This is after a couple hours of experimentation, I'm exhausted.
IMG_20150412_183510615.jpg (Click image to enlarge)
Tried it with just a vise and screwdriver, no luck. Then I slightly heated mine with a butane torch. Came out smooth.