Why is the 16th Karmapa visualized rather than the 17th Karmapa in Karma Kagyu? From what I have seen observing Kagyu ceremonies, the 17th Karmapa (either of them, actually) is treated with great awe, respect and reverence. However in their daily rituals, Kagyu buddhists usually visualize the late 16th Karmapa. I assume this is the result of a certain prescription within Karma Kagyu but I was unable to find explanations of this on the Internet.

So, why do Kagyu followers visualize the late instead of the current holders of the Karmapa office? Does this have to do with the status of the late living Buddha as opposed to the living living Buddha?
No, it is not true that it is done by the prescription of the Kagyu. I asked one of the senior students at the Dagpo Kagyu Ling center near me, who is very close to the head of that center, so he is in a position to know the answer. He told me that people can choose who they visualize during their practice, either the 17th Karmapa, Thaye Dorje, or the 16th Karmapa, Rangdrung Rigpe Dorje. What is true, is that there exists a special Guru Yoga practice text for the 16th Karmapa and not yet a formal Guru Yoga practice text for the 17th Karmapa.