Polyurethane is fine on top of well applied BLO (no gobs on the surface), but if your BLO "finish" has other stuff in it, it's hard to say without knowing what the other stuff is.
I would not apply polyurethane over a friction finish because of the wax in the friction finish. It might look fine for a while, but I think the poly will eventually delaminate. If I had to do something, I would try stripping the friction finish and then coat with shellac before applying polyurethane.
The only lacquers I use are water based and I wouldn't apply that to either a BLO or a friction finish.
Ed