It is hard to divide a single crown but very easy to layer micrphylla at this time of year. Just pull down a branch and bury it with the growing tip still exposed and forget about it. It will root pretty quickly. It is a good idea to layer prized microphylla and greggii anyway since the older crowns aren't as winter hardy in more northern zones as layered branches - that's my take anyway. This past winter could fool us all concerning hardiness and should not be taken as the norm.