I've seen at least two shab-tens for ChNNR. The one I use on a daily basis is:
By the blessing power of the Three Jewels and all of the mandalas in one
And by that of the Three Roots and the ocean of Dharmapalas,
May the lotus feet of the tamers of beings, Namkhai Norbu, be secure
And may His great aim for the Teaching and beings be accomplished without obstacles.
As for a general long-life prayer for all Gurus together, I like this one written by the previous Dzongsar Khyentse:
The primordial, all-pervasive nature of mind is beyond the changes of birth and death.
By this truth, may the lives of the non-sectarian protectors of the Teaching and beings remain steaqdfast,
And, by means of the unceasing ornament of the five times five aspects of Your Buddha activity,
May You shake all beings from the ocean of samsara.
I was taught that saying long-life prayers for the Gurus not only extends Their lives in this world but also extends the life of the person who says them. With my Root Guru, we never did any beneficial action no matter how small without 1) dedicating the merit, 2) saying the Teachers' shab-tens, and 3) saying at least a couple-few general aspiration prayers. Sometimes this felt very repetitive and pro forma. However, I have to say, that this practice has stood me in good stead these last four decades and more. In fact, I find myself saying more and more mon-lam, not less and less. But then that's just me.
Pema Chophel པདྨ་ཆོས་འཕེལ