Disabling triggers in a transaction

If I disable INSERT and UPDATE triggers inside a transaction; by
setting and resetting reltriggers in pg_class; am I correct in
thinking that this will disable triggers globally for that table for
the duration of that transaction? So an INSERT or UPDATE to this
table, outside of the transaction and within that precise timeframe,
would NOT fire the trigger? If so, would the 'serializable ' isolation
level be required in order to ensure this doesn't happen?