Your unlock means nothing to the ability to install a ROM or not.
Now, you can install the Samsung ported Sprint Kitkat ROM for AT&T if you update your bootloader and modem to the MK5 version and never use ODIN or try to downgrade your bootloader ever again ! This ROM will not work without the MK5 bootloader and modem. If you proceed that way, your warranty will be void
Also, you can always flash Koodo builds
If you wish to keep your current bootloader, you can always install any of the non samsung ROMs, but some will require that you have the MF1 bootloader at the least (CM for example).