I think it has something to do with the locked rom_col as well, it seems that core values of the map layout are locked, possibly to prevent corruption of the map images.

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Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.