ElFuego,
1) Since you now have the foam block location info from Hobie....they are a tight fit....so muscle them into place....you can always use some Gorilla tape to secure them once in place.
2 .....go to your local variety store and purchase a stick of children's "sidewalk chalk", in a contrasting color to your hull color......wipe the chalk over the S/N area several times and your S/N will be very visible
3) As Jbernier said, the lumbar BOA is replaceable, so if you destroy it as you try to release it, it's no big deal. I would spray some WD-40 on the mechanism and then yank/pull really hard the outer knob to see if it releases.
These are cheap/simple solutions to solve the issues you have described.