autovacuum on pg_catalog tables

[Zwettler Markus (OIZ)]

I would like to start a more aggressive autovacuum on pg_catalog tables like 
pg_largeobject.

So I tried as a superuser:

# alter table pg_catalog.pg_largeobject_metadata set 
(autovacuum_vacuum_scale_factor = 0, autovacuum_vacuum_threshold = 5000);
ERROR:  permission denied: "pg_largeobject_metadata" is a system catalog

(How) Is it possible to change such table attributes on pg_catalog tables?

Thanks, Markus