A simple upgrade to VMware vSphere Client 5.5 U2 regains your ability to edit hardware version 10 VMs, even without vSphere Web Client
vCenter Server 5.5 Update 2 Release Notes
Unable to edit settings for virtual machines with hardware version 10 using the vSphere client
When you attempt to perform the Edit Settings operation using the vSphere Client (C# Client) in a virtual machine with hardware version 10 (vmx-10), the attempt fails with the following error message:
You cannot use the vSphere client to edit the settings of virtual machines of version 10 or higher. Use the vSphere Web Client to edit the settings of this virtual machine.
This issue is resolved in this release.
This is great news. Finally, this age old chicken and egg problem has been (mostly) resolved. All you need is any 5.5.x version of ESX, with just the new client. You don't need a vCenter Appliance. See also the video of the installation and testing I created today, just scroll on down.
vSphere Client 5.5 U2 offers Restricted Edit of Hardware Version 10 VMs
by Chris Wahl, Sep 15 2014
Comment below this VMware Blog post vSphere 5.5 Update 2 is GA, available for download
by Harish Niddagatta on Sep 9 2014