The following bug has been logged on the website:
Bug reference: 9457
Logged by: Dylan Simon
Email address: dylan-pgsql@dylex.net
PostgreSQL version: 9.3.3
Operating system: Linux
Description:
It would be nice if there were a way to change the query definition of a
matview, presumably with "CREATE OR REPLACE MATERIALIZED VIEW". Obviously
the same restrictions on replacing a view could hold. I haven't seen any
mention of this as a planned feature or anything that would prevent it.