G'day,
I am just back from Portugese Camino. I used a pair of Merrell boots but also took a pair of sports innersole inserts, just in case, as in training beforehand I had some issues with shin splints when switching between my runners and boots. In training I experimented with the inserts and they seemed to help but nothing really definitive.
As it worked out I started out OK with my boots for about 5 days but then, after mild shin splints, replaced the inner sole with the sports inserts and walked on with no further problems. I think Albertagirl has some good tips, so just try out the various combo's before you go and then when you are on your Camino you'll have some ideas to sort any issues. In my experience of the Camino what worked at home may not work on the Way so look after yourself and go with the flow.
Bon Camino