Is there something similar to the lib/autoload folder, but for SQL scripts?

My use case is: I have a bunch of UDFs. 

A SQL script defines their SQL interfaces The script is in lib/createdb.

Sometimes I make changes to those UDFs, and their interfaces need to be updated. But my the script is only run on DB creation, so I have to manually go thorough all existing databases and run the script. 

The script is in a way idempotent, because it uses CREATE OR REPLACE, so I don't mind running it every time the database is started. But I can't find a way to do that.