Also, don't forget to test for relkind = 'r'. My bad from before.
Revised query is below.
SELECT 'ALTER TABLE ' || quote_ident(n.nspname) || '.'
|| quote_ident(c.relname)
|| ' ALTER COLUMN ' || quote_ident(a.attname) || ' TYPE varchar;'
FROM pg_class c
JOIN pg_namespace n ON n.oid = c.relnamespace
JOIN pg_attribute a ON a.attrelid = c.oid
JOIN pg_type t ON t.oid = a.atttypid
WHERE t.typname = 'bpchar'
AND c.relkind = 'r'
AND n.nspname <> 'pg_catalog';