If you are running a stock rom, rooted, unlocked/locked bootloader with stock recovery, you will lose the ability to unlock the bootloader if you accept the update.
If you haven't received the update you can do several things to prevent the update from flashing successfully:
1) Load an alternative recovery like TWRP on your device. Having an alternate recovery on your device practically guarantees any stock OTA software will fail to install.
2) Disable the following system file (SDM 1.0) via Titanium Backup's Freeze option, or use Root Explorer to rename the file name in /System/App to SDM 1.0.bak
If you haven't received the update you can do several things to prevent the update from flashing successfully:
1) Load an alternative recovery like TWRP on your device. Having an alternate recovery on your device practically guarantees any stock OTA software will fail to install.
2) Disable the following system file (SDM 1.0) via Titanium Backup's Freeze option, or use Root Explorer to rename the file name in /System/App to SDM 1.0.bak