I recently went to the LEGO Store to buy a Star Wars C3PO minifig, but he was only available in large kits and I couldn't buy him separately. I was told that they had the astromech in keychain form, but you can't remove the head or the legs. Not to be denied the driod I was looking for, I bought him and decided to try and remove the key chain myself. A little Internet searching revealed that many people have had this exact same problem, here's how I solved it.
Removing the key chain from your LEGO minifig is easy. After, you'll be able to switch out heads or add your favourite hat. All that's left is a small opening where the friction fit pin was; this small opening can be filled in with coloured putty or some other type of filler and painted to match.
brute force method: paperclip pliers cloth Using pliers remove the chain portion from the minifig so that just the pin with the eyelet remains. It helps to know what the pin looks like so you know what you are trying to remove. The pin is ribbed, then friction fitted through the head and neck, then into the torso. A paperclip was inserted into the pin eyelet and grabbed with the pliers, the minifig was wrapped in a cloth to provide extra grip, then the pin was pulled forecfully pulled from the minifig. If you are having trouble try immobilizing the minifig by clamping it do something sturdy (like your workbench) or by putting the minifig in a drawer and pull the pin out upwards. This is not the only way to remove the key chain pin. Here are two other ways:
cutting method: heavy cutters / rotary tool The pin can be cut at the top of the head with a rotary tool or heavy cutters. This will produce a clean surface, but may require some sanding to smooth down entirely. The disadvantage here is that you may grind off a portion of the head while removing the remaining portion of the pin. The silver pin top can be painted to match the minifig
soldering iron method: soldering iron After removing the chain, insert the top of your soldering iron into the eyelet of the pin and let it heat up for about 10 seconds. Then, pull out the pin. What's happening is the soldering iron is heating up the pin and allowing the pin ribs to soften the plastic around them, making pin removal easier. The major disadvantage here is that you can easily melt/deform your minifig from overheating the pin or from the soldering iron tip touching the plastic. I recommend the brute force method, as it has the least likely chance that you are going to mar your minifig. It does take some force to remove the pin, but is a cleaner method. Also, after you've removed one pin all successive pins you remove will be easier, since you will know how much force it takes to remove the pin.
I hope this helps you transform your keychain minifig into a playable addition to your LEGO set. Remember to show off your completed key chain removal minifigs in the comments below!