How to assign and specify a universal ID to custom and standard attributes

Hello,
how do I specify the universal ID? In the example "Employees API: Universal ID is now exposed" it looks as you can define the ID. Seems not to be composed of the label field
"dynamic_153804": {
"label": "Address, postcode",
"value": "",
"type": "standard",
"universal_id": "postcode"
},
Is there a way to replace then dynamic ID by the universal ID when working with the REST API? Consider a scenario where you need to convert JSON into XML for further processing. At the moment you'd get the XML node
<dynamic_153804> ...
The XML would be a lot easier to read/process if the node name would just be the uinversal_id

Thanks