Almost everyone who has cracked an SE has had the same experience. I'm afraid that you need to be quite brutal to prise the connector apart. For obvious reasons, avoid using a metal tool to do this. But it needs to be rigid, very slim and be unlikely to cause damage if your hand slips. A difficult combination of attributes...
When you have removed the power connector, ask yourself a few questions. Am I going to throw this Mac around? Am I going to transport it in the back of a car for long distances? If the answer is No, just cut off the security tab on the power connector. The Molex is a firm fit and will work fine without the security tab in normal use. The biggest threat to the life of your Mac is quickly releasing the tab and swiping the yoke of the CRT with the back of your hand.