You can edit the .vmx file and change the line: virtualHW.version = “10″ will become virtualHW.version = “9″
You can read in more detail on this site How to Downgrade VMware ESXi 5.5 Virtual Machine Hardware Version to 9 from 10
After the change in the .vmx file you have to remove it from inventory and add it back again or maybe you could reload as suggested in this link http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1026043