So a couple things
1) If all the West epoxy has cured completely then all your doing is a physical bond. Rough up the surface with sandpaper and have at. It would be a similar bond as you have between the cured epoxy and varnish.

2) If it's not cured. I'd call Raka and ask. I think the epoxies are probably chemically similar enough that you can get a chemical bond, but the guys @ Raka would know for sure. so YMMV.