If you haven't got one, go out and buy a 10/11mm pipe spanner. Sidchrome make a good one that is about $15.
Spray plenty of WD40 onto the fitting where the softline transists to the hardline. Let it soak.
Put the pipe spanner on the fitting, and undo. If you had the same problem i did, you'll quickly strip the hex head.
To avoid this, buy a cheap 10mm/11mm ring spanner and cut a slot in the end that fits the spanner so the hardline can pass through.
Once it's on, clamp the other end TIGHT with a pair of vice grips so the ring spanner is clamped hard onto the fitting. With any luck, the fitting should undo and be undamaged.
Then it's as simple as swapping the lines over, putting the correct retaining clips in and using the pipe spanner you bought to re-tighten the hardline fitting. Don't over tighten it cos you don't want to strip the threads. Usually another 1/8th to a 1/4 of a turn past tight is sufficient.
Then bleed the brakes.
No thread sealant should be used on any of these fittings either.
2 copper washers are required for each caliper, one on top and one below the fitting to ensure a leak proof seal.