You can modify the VirtualHardwareSection at once:
<Link rel="edit" type="application/vnd.vmware.vcloud.virtualHardwareSection+xml" href="https://<ip>/api/vApp/vm-9b3ad0ef-0535-4edc-b593-7f85c2bdb749/virtualHardwareSection/"/>
Retrieve a VM and inspect its links. Read the API Documentation for more information - "Configuring vApps and Virtual Machines" on page 86.