I just pulled out all the inserts in mod keys. It took me about 20 minutes.
Those inserts are glued in, but it's not some crazy glue. I think the purpose of the glue is just keep the insert tight so that they won't fall out easily. I can actually lift the insert a little bit with my hand, after that, I put a flat tweezers between the gap and gently lose the insert, just like Kirfloof suggestes.
Thanks all for your help. Now I can enjoy this set more.
![Wink ;)](https://cdn.geekhack.org/Smileys/solosmileys/wink.gif)