Removing virtual hardware resources (vCPU, vRAM, vDisk, etc.) is not supported (similar to moving from a more powerful server to a less powerful server, such as MCS 7845 ⇒ MCS 7825). These migrations require backing up the application, reinstalling on a new OVA file, and and restoring the application.
Just an FYI. Every time Unity boots, it checks the hardware it is installed on. Unless you have an exact match to an OVA template, it will tell you you are running on unsupported hardware. You have to accept an agreement that you wont call TAC for support, and then it will continue to boot. None of the other products (CallManager, Presence, UCCX) do this.
As silly as it sounds, that even includes adding more hardware than is necessary.