Did you read the page
where I discuss how the muscles "steal" the stress when they are warmed up? I use the analogy of elastic bands: if you have two elastics hooked up in series, with one being really flexible and the other stiffer, when you stretch them, it is the more elastic muscle that moves the most. This is what happens when the muscles are warmer: they will use up most of the stress of the stretch in their elongation, leaving less stress on the tendon and ligament.
The usual critique of this analogy is that the muscles with their tendons are not in series with the ligaments, they are in parallel, however recent studies have shown that this is not true. Muscles/tendons are in fact in a series arrangement with the ligaments and my example of the two elastics does represent what happens. See the work by Jaap van der Wal
in which he demonstrates how we have had this all wrong and that corrections are needed to the anatomy books: muscles are not in parallel to ligaments, they are in series, and if you warm up the muscles, there will be less stress on the connective tissues.
This is why I recommend you don't do Yin Yoga after yang yoga IFF your intentions are to get the most benefits physiologically.
You are also asking if this could be dangerous for the connective tissues: maybe. It really depends upon the student: for some students, a full yang class of stressing tissues deeply followed by a deep yin class may be too much. I invite you to re-look at the Goldilocks
article I wrote a while back: you will see that the cumulative stress does weaken our tissues and we could cross the point where damage can occur. When you are loose, you are closer to the breaking point. In the same way we advise pregnant women not go too deep in a pose because of the hormone relaxin flooding their system. They may be too flexible and too close to the danger point of hurting themselves. But, for many people, this won't be a problem so it is difficult to generalize. The key is to get the student to check for herself: what are you feeling? If there is any tweak or pain, come out.
I hope this helps.