First reaction is +1 for finally switching to real constant nodes in the AST for 3.4+. This is an inherited behaviour from 2.x where these were ordinary names rather than true keywords, so we weren't able to completely disallow overwriting them.

As a smaller impact change for earlier versions, we should be able to do something in compiler_nameop [1] that picks up the 3 singleton names and allows only LOAD_CONST, erroring out otherwise.

http://hg.python.org/cpython/file/default/Python/compile.c#l2625