those plugs are called shear bolts, when they get to their torque limit the bolt head shears off leaving a plug lookin thing behind, makes it harder for crooks to frig with your steering lock but makes it a complete bastard to remove them when you need to, I used a small cold chisel and smacked a groove in the plug ends then undid em with a screwdriver, the cold chisel tends to loosen em up a bit too.
Im pretty sure you can remove the barrel via a small hole in the housing but i think its gotta be in a certain position to work( usually a position you cant get to without the keys) but dont quote me on that, its been awhile
