#WARNING: THIS COULD POTENTIALLY MAKE YOUR COMPUTER UNUSABLE IF THE FIRMWARE DOESN'T WORK PROPERLY. Please make sure you know what you're doing before continuing.#

Manually Flashing The Firmware

1. Download the firmware installer.
2. Unpackage the package. Find the installer app.
3. Locate the firmware within the app's contents. It'll have a name like "MB51_007D_03B_LOCKED.scap"
4. Run this command sudo bless -mount / -firmware /Applications/Utilities/NAME_OF_FIRMWARE_INSTALLER.app/Contents/NAME_OF_FIRMWARE.scap

This should restart your computer and flash the firmware.

Change the Version of OS X Your Computer Thinks It Has

1. If necessary, turn System Integrity Protection off.If necessary, turn System Integrity Protection off.
2. Reboot into Recovery Mode
3. Open Terminal under the Utilities menu
4. Type csrutil disable
5. Navigate to and open /System/Library/CoreServices/SystemVersion.plist
6. Change ProductUserVisibleVersion and ProductVersion to a valid version of OS X (such as 10.9.5)
7. Optionally, reverse the steps above (csrutil enable for SIP back on)