If your code is already using the new BIT VARYING representation, you don't need to change your code. You'll just need to reinstall because the functions which do key manipulations (found in postgresql.sql) now spill over to 31-bit rather than 15-bit long key.
If you're converting from the old varchar + LIKE style you'll need to change the triggers on your type and switch to the BETWEEN style comparisons (I'd done this for the varchar keys some time ago since the LIKE style doesn't use the index on the varchar sortkey). Take a look at some of the queries using tree_ancestor_keys. Just grep and look, the usage is very straightforward even if the path we took to get here is not :)
