Hi JP-
I think what David is getting at is to make a new composition with a resolution of 720 and import your 1080 GoPro footage to that comp.
You’ll have to scale down your footage to get it to fit in the comp so once the footage is in zoom out on the comp and select the clip so its bounding box appears, hold the shift key and resize the footage to fit the comp.
Alternatively, you can right click on the clip and select the Scale option in the Transform menu. Reducing the size to 67% will get you close enough, 720p being 2/3 the size of a 1080p shot.
In the end you’ll have the 1080 resolution in a 720 frame giving you the room to zoom on the face without loosing quality.
I’ll shoot this to you in an email as well.
James