About

Header Transformation Rules are used to modify or add headers.

Header Transformation Rules are available in the Routing section.

Create

Press ADD NEW to create Header Transformation Rules Group.

The image below shows which headers are possible to modify.

Depending on the header, it is possible to:

Forward without changes - no changes to headers.
Transform and forward - modify the current header.
Transform existing, generate if missing - modify the current header if it exists. If it does not exist, a header will be generated.
Overwrite - drop the original header if it exists and create a new one.
Drop - removes the header.

It is also possible to add a custom header to the empty header field.

When rules are created, they should be enabled at Termination Point settings: Termination Point Signaling Settings

Kamailio Transformations are used to modify headers. More information here