LG Optimus 4X HD's bootloader finaly opens
We should let you know that shoehorning ROMs on the LG Optimus 4X HD is a bit more difficult than doing so on other smartphones. This increases the risk that something could go wrong. Keep in mind that simply unlocking the bootloader is grounds for voiding the warranty on the phone. But besides that, there is always the chance that you might end up bricking the device and while a nice looking paperweight can always spruce up a plain looking desk, that is not the intended purpose of the device. Make sure you know what your doing before you even start.
source: XDA via AndroidCentral