As your requirement is in REST Service i would suggest you to go through the below discussion which talks about converting clipboard page to json(without pxObjClass) and you can write custom code accordingly to achieve it for Page List.
Basically I want to add the text "ReqResults" to the json. Please find attached a sample of current results. The results are in pagelist and Map From key is that pagelist and Map From as JSON (for REST Service)
How could I format the JSON string from Rest service activity?
The REST service invokes the activity which sets the results in pagelist. Since Map From is JSON, the results are converted into JSON format. So in order to append the string, it should be after mapping to json? If this is right, can it be done in the service activity itself? Sorry to sound so naive, but I'm new at this.
My thoughts - this append cannot be achieved in the service activity because at this stage the results are in pagelist and a text cannot be added to pagelist property. So that leaves the formating to be done post-mapping. How can I do this?