Is it a bad practice to query pg_type for enums on a regular basis?
What @Jack said. Plus, if all you need is the list of registered values for an enum type, there are some Enum Support Functions to do that. Based on Jack's example:

SELECT enum_range(null::mood);

enum_range
--------------
{sad,ok,happy}


That's simpler and resilient against (unlikely) changes in future major Postgres versions that might break your query.

dbfiddle here