I'm afraid I don't understand the problem that you're describing - could you clarify?
Normally, for a machine built from an image, removing the agentguid registry value is enough - when the agent starts, a new GUID is created, and this allows ePO to identify the machine as a new machine... so if entries in ePO are being overwritten, then something else is happening.
I would recommend not installing an agent on an image. If you are sure you want to go this route, I would just do the agent. Let ePO do its job and deploy the other products otherwise.