Winds of Chaos

The party's Elven Mage is learning another discipline/wind and is effectively going back to being an apprentice to do so.

If he wants to learn a spell that he already knows (ie blast) but in the new discipline would this still qualify as learning a new spell?

yes, it's technically learning a new spell because it has to apply the new discipline's channeling and school effects. cantrips do not have to be learned for each school but the rest do.