There are several things that happen when you do a clone-prep-clear-config. But here are the main things concerning the host.
First, checking out the help section for the command from a command line yields this:
./splunk help clone-prep-clear-config
Clear a Splunk instance of instance-unique config parameters, which are normally created on initial startup (first-time run, "ftr"). Intended for use after an instance has been cloned (i.e. all its files simply copied) from another instance.
There are 3 main files that get the hostname and GUID cleared (remember, there is more than just this going on):
inputs.conf (the host key in the [default] stanza is cleared)
server.conf (the serverName key in the [general] stanza is cleared)
instance.cfg (the guid key in the [general] stanza is cleared)
In addition to these things, a 0-bytes file named cloneprep is created in the $SPLUNK_HOME directory.
When the Universal Forwarder starts back up (which will happen after PVS or MCS has assigned the hostname and system GUIDs), all of the information is filled into the 3 files mentioned above and the cloneprep file gets deleted.