Will you be able to sing medieval organum as well as Brigitte Lesne and the French women's Ensemble Descantus? The short answer is "No."
HOWEVER, you will understand the roots of Western sacred music by having the thorough knowledge of Gregorian chant that the CMAA Chant Intensive will give you. You'll understand notation, principles of rhythm, the relation between text and melody. You will be able to look at a chant and give it a go. And then you can explore the glories of organum with a solid foundation.
Why not register now?
In the meantime, here's a wonderful Alleluia from Ensemble Descantus. And no, they don't look like the picture. They're quite chic and French. You can find them on Facebook and see what they're up to now.