In this case the marked paths does not allow bikes and I want to create a route avoiding them. That is the thing, it is not bike specific but needed anyway to create a bike route. (it is the city running paths in the example above. Not only off limits but heavily trafficked).
I had resigned to adding them manually to basecamp but I noticed on RWGPS that this layer has exactly what I need.
Maybe brouter is an alternative for you: http://brouter.de/brouter-web/
I don’t know if it uses the marked ways or not but it is highly configurable.
A Garmin map (for Basecamp) with special routing avoidances probably requires mkgmap with a custom style.
Brouter has the exact same info but nicer looking. In the hiking overlay.
I dont see any layers or such in basecamp.
It is more about visual information rather than routing.
I did consider going down the mkgmap rabbit hole but I probably better just spend 30 minutes drawing it in manually in basecamp and be done with it.
For the moment at least it is just in this very small area I need it.