I've changed just offense (also with 6 freshmen) and made the PIT (with some solid senior play helping out a lot). Their sophomore year, however, I did not make the postseason (ended up around 100 in the projection report as I recall)

I'll get back to you when I know. Their JR year is next season in Knight. 

I definitely wouldn't change just because they don't know what they're doing. It's not like their IQ is off the charts in the other defenses. But if you want to change anyways, this is as good a chance as you'll get. What I did was practiced the new defense for ten games but played the old one, and then switched over to the new D for conference play.