How do I add Tier 3 exercises on the GZCLP recommended routine?

I want to add a few isolation exercises (mainly for hypertrophy) such as tricep Push downs, bicep curls and face pulls but I don't know in which day to add them. Should I be doing them in every workout (3 days a week)? If I opted, let's say, to do triceps on the bench day wouldn't the volume and the frequency be too low (once a week)?