I also walked both of those alternatives this year. I would only caution that there is one unmarked intersection on the first alternative, close to the merge with the "official camino" at Zas. I guessed correctly, and went up, but a Dutch woman I met guessed wrong and went down, and she wound up having to walk a few extra kms, all on the road, to get back on track.
I particularly liked the river alternative out of Negreira, it was far nicer than the asphalt trek I remembered from previous walks out to the coast.
And just one last thing that occurred to me when I was looking at the signs-- they were obviously new and recently installed. But these signs would be much easier to vandalize and rip down than your standard camino mojón, so I hope the teenagers and other vandals keep their hands off! Buen camino, Laurie