If you do not want custom roms anymore, then accept the OTA.
If you want to continue using custom roms then do not allow the OTA to install. Freeze the system app "sdm 1.0" using Titanium Backup OR rename it to "sdm 1.0.bak" using a file explorer. This will cause your Software Update setting to force close anytime you try to manually check for updates. Now, go to /Cache and delete the update.zip in /FOTA
More info in the TW 4 3 discussion thread: http://forum.xda-developers.com/show....php?t=2575661
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[VZW] Samsung Galaxy SIII