Yealink provides a Configuration Generator Tool that can help you with fast and easy custom configuration generation, modification, conversion and encryption. You can download the tool at support.yealink.com.
Caveat: If you are using the Yealink Configuration Generator Tool, the labels can be a bit misleading. If you use their CGT please note that the Extension is for pickup code, the value is for the PBX extension you want to subscribe to. E.g.: