gistfile1.rb

json = {
    "component": "root",
    "body": [
        {
            "component": "headline",
            "text": "42323"
        }    
    ]
}

class Hash
    def insert_uuids()
        if not self.is_a?(Hash) and not self.is_a?(Array)
            return
        end

        if self.is_a?(Hash)
            self[:uid] = 'some random uid'
        end

        self.each do |arr, val|
            if val.is_a?(Hash)
                arr.insert_uuids()
            end
        end

        self
    end
end

puts json.insert_uuids()