Broken pg_class table

I accidentally wrecked the pg_class table in a database by leaving off
the where clause of an update statement when setting the reltriggers
back to the count from pg_trigger after a bulk data load.  I can no
longer connect to the database, although it does start up without
error.  running psql [dbname] causes extreme cpu load, and the command
just hangs.  Memory usage continues climbing until a oom killer crashes
everything.  I presume that my blunder is causing some sort of infinite
loop during postmaster startup for the spawned process.  Is there a way
I can get direct access to the file for pg_class and reset the
reltriggers to the correct values without a full dbinit process?