The apk and odex files to disable the Unknown SIM warning are VzwPhoneService.apk and .odex.
I haven't run any custom ROMs on the M so I am not certain what the problems might be with 4.4 versions, but I can talk to dhacker and see if he is aware of any specific issues and/or fixes for GSM service. This hack unlocks the radio itself and has nothing to do with the ROM, but the ROM has to support the radio properly for services to function, obviously. The apns_config.xml is a typical problem that needs editing but there are other RIL libs and binaries that need to be there as well as build.prop configurations that also need to be set for everything to work.
None of that can work at all until the radio is unlocked in the NVM first though.
Digital alchemy for the Droid and beyond.