I re-did the hard pipes on both my rears but had an arse of a job getting the flare nuts apart.
If, like me, you realise there's no saving the pipework then just chop it in the middle and get the caliper off to work on it - it's so much easier!
I had to use a lot of heat on my inboard flare nuts (hard to flexy joint) but if you're careful you can do it without shagging the rubber pipe. Likewise don't be tempted to try to ease the flare nut out of the caliper without using heat to loosen the joint. DAMHIKT.
Invest in a brake pipe flaring tool - I got a kit
like this which gave me the right flare nuts and enough copper pipe to do everything on both sides - twice! I also re-did the link pipes on two of my calipers. The flare tool gave me some slightly eccentric mushrooms but despite not looking as uniform as the factory item they've held hydraulic pressure ok.
You need to think about routing the copper pipe around the trailing arm - leave yourself plenty of extra length for the kinks and bends you'll need to make to get around the casting and for the final bend into the caliper. Put the flare nuts on before bending and flaring lol...
It's not difficult - I'd not done it before and it was a relatively easily achieved objective.
Good luck!
Forgot to say - don't try to get the flare nuts out with a normal open ended spanner, there's too great a risk of rounding the nuts - look for a proper flare nut spanner, I think it's a 12mm and they're about a fiver from Halfords...