Pin lesson to date

I have an ongoing curriculum unit, but I sometimes pause for special Friday activities. I would love to plug in all of my Friday activities in advance, but I can't easily do that because I am frequently bumping and adjusting my other curriculum unit. Every time I make my adjustment, it moves my Friday lesson to the wrong date. I would love to be able to PIN the lesson so that I can bump and pull back other lessons without affecting the pinned lesson.