Many if not most of the subroutines in Vinyasa Krama can stand alone and we can mix and match these subroutines to form a practice that suits our requirements. Some though are clearly advanced developments of postures and require some preparation.
Kurmasana is a challenging posture, the tendency when we begin to reach around for our ankles is to fall backwards, the hands behind the back utkatasana posture is good preparation here. Good engagement of the bandhas as outlined in Day 4 ( ardha utkatasana ) is helpful, keeping the chin down while working first one and then the other hand around our ankles makes it a little easier too. Once we have a good grasp of our ankles we can then release jalandhara bandha, the chin lock and look up. Of course it's a good idea to lower the chin again before unclasping and returning to standing back through utkatasana.
Another tip for reaching around for our ankles and ultimately to clasp our hands behind our back is to stretch up out of our pelvis and keeping that stretch as we lower into utkatasana. Feeling longer we can then stretch further beyond our knees giving us more room to reach around our knees.
A tip for malasana, as you lower your head towards the mat raise your thighs off your calves. Lifting your backside up allows your to lower your head more carefully to the mat, less chance of tipping forward, then when your forehead is settled lower your thighs back to your calves while keeping your forehead on the mat.
The final kurmasana variation entails a rounding of the back to bring the crown to the mat.