In case anyone else ends up here. Better solution exists now.

Microsoft documentation for list of functions for both JSON and XML - HERE

addProperty - Add a property and its value, or name-value pair, to a JSON object, and return the updated object.

coalesce - Return the first non-null value from one or more parameters.

removeProperty - Remove a property from a JSON object and return the updated object.

setProperty - Set the value for a JSON object's property and return the updated object.

xpath - Check XML for nodes or values that match an XPath (XML Path Language) expression, and return the matching nodes or values.