Dental #: cerec is for crowns/margins at the gumline. Can itero work for my below the gumline crowns when a new replacement crown is necessary?

Perspective-->. Any crown can be placed at, above or below the gum line. That is not dependent upon the crown material but at the discretion of the dentist and his\her philosophies and specific circumstances of your case.
Crowns. Cerec and itero are digital systems to design and build crowns. Cerec is a system for in-office single visit crowns, while itero data is sent to a dental lab to make the crown and a temporary placed while the crown is made. I am a cerec dentist and crowns can be made for under the gumline as long as you have control of the bleeding to get images. With good images a crown can be made.
Cerec, itero, e4d. All of these devices are used to capture images of the tooth above or below the gum line. As long as a good image is made, any type of crown can then be fabricated from that image. Sometimes that is in the dental office and at others it is in a lab. The best type of crown should be determined by your dentist.
Yes. I tero can work as long as the dr. Gets a clear picture of the margin on the crown that is below the tissue.
New is not better. Many of the newer items unfortunately are really still in the experimental stages and do not give very good long term success at the margins.