Yes you can switch off alarm and immobilizer at the BECM.
Yes your fob will still lock and unlock the doors and boot and turn on the courtesy lights and a long press on fob's "lock" button will still lazy close the windows and sunroof.
Your car will never again lose ECU sync. It seems to stop looking for it. I mean I think. It seemed to work for me.
You can do this by changing the region setting to Middle East or Gulf or something. It might work with other region settings too but here at least the display language remains Englishinstead of Finnish or Swahili or something! If you can access the settings have a play. The only problem is having insurance once you've disabled alarms etc. That's why Datatek's idea is brilliant. Do the above and fit an insurance approved aftermarket kit. Alarm and immobiliser suffice, doors etc still work as just described.