Rewiring the EX box is almost as odious a job as rewiring the internal routing, just slightly less tedious. You still have the same problem that every time you get it wrong, you can't reuse the wire, or any of the fiddly bits, so you'd better have spare cables and fiddly bits at the outset, before you start.
I have only ever cabled up two EX boxes. And I managed to get it wrong both times
* In both cases I was able to carefully retwist the cable end and refit, so do not despair folks; you can get a second chance
* Left the barrel adjusters out after the measure/cut phase
With the wife's bike I even managed to get the cables swapped so her top gear is 1 and bottom is 14. I thought a third-bite at the cable-ends was a bridge too far. Every now and then I suggest that I should "fix up her gear shifter" but after riding the bike for 6 years she says "NO...... don't fiddle with what ain't broken!!"