Hi
Sounds like a great idea.
I am on my Camino del Norte (in stages) and have walked the Camino Ingles already.
I had already a similar thought. I considered to stay on the coast or cross the mountains to reach Ferrol for the Camino del Norte.
How much time do you have? By bus it should take a day only, on foot it might be a week.
It would give an opportunity to visit also the pilgrimage shrine of "San Andres de Texeido" at the Galician coast, north east from Ferrol (roughly 35km), There are reportedly Europe's highest cliffs to the sea.
There are a few pilgrimage days during the year, the most important is the 8th September when the dead are remembered.. Otherwise probably pretty remote.
It must be quite an interesting place to visit. It was pre christian site of worship. St Andrews allegedly landed there (when his boat capsized).
There is an old saying in the area "If you don't visit San Andres de Texeido alive, you'll go des (A San Andres de Texeido vai de morto o que no foi de vivo), but you could be reincarnated as a bird, lizard, toad or snake.
I believe that a walk along the north coast to come to Ferrol would be a great adventure.
The Spanish have a great passion for walking and there will be a number of marked ways. As not a pilgrimage route it will require flexibility regards accommodation (Casa rural, hotel, motel hostels and possibly campsites)
The way from Ferol to San Andres de Texeido joins/departs from the Camino Ingles near Naron - 7km from Ferrol, signposted with a red outline "fish" symbol.
If you have a week spare go for this great adventure