This wiki will tell you how to make elements on some levels unselectable using Select By Attributes tool.
When we set Level Lock On, only the elements on active level are unselectable. Then can we make elements on some specified levels unselectable? The answer is YES.
If you want to back to normal status, you can set Mode to Inclusive, Location, Off in Select By Attributes dialog and then press Execute button.
[V8i C++]How can I disable locate by Levels