Never done any on a muzzy, but you can normally do MOST of the plugs, on most cars without engine removal.
However, most core plugs [frost plugs] are often under exhaust manifolds and other really hard to get at places, or covered by other components.
On most cars there's often one behind the flywheel, not too easy.
Getting them out isnt too bad, but you will need a good area of swing to drift the new ones in, you cant expect to just flip them in.
From what i've seen on mine, taking the motor out might be the easiest way, unfortunately.
I assume your losing a bit of coolant? If it had blown straight out, you would know, you might as well just pour the water straight on the floor.