Joseph, that's one interesting issue because very often I use the same lesson in another course with different students.
So, we have to adapt the lesson to the new "class". lesson's should have a menu similar to the quiz, because we can mix the parts in another adapted way.
Weel, I do it in two ways (not completely satisfactory). I use MOODLE 1.9. Perhaps someone could share another ways to do it.
1. In one lesson, I create one deadzone with the group/endgroup option, where I keep all the parts that I don't want to use in that particular lesson. Whenever you make the backup, you can remix the parts.
2. If we use shorten lesson's, we can mix it by showing or hiding in the lesson, but this need a well defined context/documented for the lesson's; if not you just don't know why and for what type of students you use it.
I hope this is helpfull.