These modules are constructed in a delightfully simple way - a solid "chassis" is wrapped in thin steel, and these press-tabs are pushed in once assembled to hold the outer shell in place.
There is one of these push tabs on each side, though they're not quite aligned. They're tricky to get out, but if you're careful, you can poke something thin all the way through!
The best way I've found to open these up, is by inserting something from one side, and pushing these tab out on the other side.
I've previously used a paperclip, but it bent and was a little large... today I modified a needle by cutting the eye. I actually left the fingers a little long - I have three modules to disassemble, and one of the fingers broke off part way through the operation... they can be much shorter!