Don't know what reticle you are wanting to go with, but the following quote is from the Zeiss web site.
Retrofitting Rapid-Z® Reticles
Please be advised that there is currently no available option to retrofit the ZEISS Rapid-Z® reticles into previously purchased ZEISS riflescopes with a standard reticle. This is to ensure that customers who want to purchase a new ZEISS riflescope with the Rapid-Z® reticle are given priority attention. We thank you for your understanding.