This is happening because your function is under characteristicsValue[] array and the CopyFrom function cannot be currently told to modify only subset of the items. If you need this behavior, you need to use scripting. JavaScript and C# languages are available.

Thanks for the suggestion. Can you please share a sample script for this behavior in JavaScript? so that we will follow the same . 

Thanks for the suggestion. Can you please share a sample script for this behavior in JavaScript? so that we will follow the same . 

In the script, you can use "Script/Insert Path" to interactively select the node you would like to work with and the address will be filled for you.

The script could look like this:

hpsv.response.memberSearchResponse.memberSearchResult['Member[]'][0].memberId = hpsv.request.memberSearch.name.firstName;

Please be aware, that above script is just modifying existing value and the response structure must exist before the code is executed. If you are setting the static response in another rule, you should be OK.