I don't think the 4.2 falls under the ceramic glow plug issue.
Get the car nice and hot and use some plus gas soaked in for a while round the thread, I'd be inclined to buy a 1/4 torque wrench and use the ceramic glow plug torque values for undoing to save yourself headache.
My ceramic plugs came out ok on my 54 plate 3.0tdi, you may find yourself backing the plugs back in and then undoing a few times before they will release properly, spray more plus gas whilst doing this, the carbon jams the tip and this is what causes breakages, so in theory a good dose of carbon deposit cleaner run through the engine before removal may also help
