One of the great things about mechanical and custom keyboards is the ability to carry time saving and ergonomic macros and shortcuts from one system to the next. But if you don't have a keyboard that supports layering or customizing keycodes, you can use software and the OS to cover some things, but they don't carry from system to system.
Turning the capslock key into a control key is a huge time and finger saver at the mere cost of yelling at people who are wrong on the internet, and is a common request for what ever operating system you're using.
The problem is if you find yourself on a system that doesn't support the keymapping or makes it very difficult.
So why not skip the software, and turn your caps lock into the exact same keypress as your control key on your keyboard's circuit board?
Step 1: Open It Up!
I'm working on my CM Storm QuickFire Rapid, and voiding your warranty is just one screw away!
Cut or remove the warranty sticker with the "OK" on it and unscrew the one screw.
Then slide a soft thin stick along the seam to unhook the short clips holding the top to the bottom. The two pieces seem to be under pressure, and as soon as the clips are out of their slots, they stay there, so don't worry about them snapping back in place.
Detach the daughterboard with the USB jack on it from the primary board by pulling/wiggling the white low profile plug out of the slot.
Step 2: Confirm Your Key Connections
CM prints the keys on the back of the circuit board, so they're easy to find.
Identify the lead which connect to the key switch and NOT the diodes or other elements.
You can test them by using a connectivity tester and pressing the key.
These are the leads we're going to wire to the control key below
Step 3: Break the Tracks
In order to make the capslock key not a capslock key without messing with the signals coming from the key, we need to isolate it by breaking its connection to the rest of the board.
We'll do this by destroying the copper track that runs from the switch leads to the rest of the board, effectively disconnecting the switch.
Don't be afraid of this, the tracks are easy to repair or bypass if you want to undo this later.
After a few false starts and overtravel, I found the best way to do this was to stab a pointy knife into the circuit board, then tap the spine of the knife with something semi-heavy and metal like a wrench to walk the blade forward a little bit at a time until you've made it across the track. (Don't use a knife you like, circuitboards are made of fiberglass which will damage your edge)
Test with your connectivity tester to make sure the track is broken there, and other elements are still undamaged.
Step 4: Solder!
Short the connections to the caps lock key down to the connections for the left control key.
You've basically made the capslock key fully equivalent to the control key, just in a more convenient place.
Enjoy your convenient control key no matter where you plug in!