What is the safest way to remove cartridge clips ?

First, unscrew the cartridge and then stretch the wires easily before removing the clips one by one.

I like to use a pair of straight surgical sutchers. I attach them gently on the flat part of the wire just below the pins and then gently pull.

You're right. It's all too easy to break those wires (not the pins, though). Take it slowly, have good light, and secure the arm as well as you can. If the cartridge clips are not too tight, you can ease them off the pins with tweezers or needle-nose pliers. If they're tight, I have more luck inserting the tip of an x-acto knife between the cartridge body and each cartridge clip and sort of pushing the clip, gently, until it is free of the pin. Good luck. Once you do this a couple of times you won't be as concerned, but you should always be careful and gentle.