Hello,
We do a similar change for register codes. In this process, we use ISU_S_DEVICEMOD_PROVIDE to get the initial data and then ISU_S_DEVICEMOD_CHANGE to make the update. In the exporting parameter x_auto, we send the necessary meter read information. It's in a structure called x_auto-meterdoc-eabl.
The ISU_S_DEVICERATE_CHANGE module appears to have the same structure. Perhaps either you should call ISU_S_DEVICERATE_PROVIDE first to see if it will pull in the necessary meter read data, or you can try manually populating the meterdoc data in the change call.
Regards,
K--