Can custom avoidances be set in Bese Camp - area avoidance or road avoidance? There is such setting in MapSource under Edit -> Preferences -> Routing -> Advance but I couldn't find such in Base Camp.
I think the OP was asking about custom avoidances such as avoiding a particular stretch of road or a specific area. I don't know if that's possible in BC but you can in Mapsource. If it is in BC I can't find it. Maybe FALAGAR will stop by with a better answer.
DIMITARDIMOV is right, Mapsource had a really great advanced area/road avoidance settings that are, I'm sorry to say, just not in BC. Hopefully in a future release.