As far as I know, re-installing P5 will not overwrite your current P6 installation.  It will install into its own folder.  It has been true with all version after P6 and it is still true with P8.  If there is no absolute way to retrieve the P5 content off your disk, I would recommend a temporary reinstallation, copying it's runtime content to a new folder, then delete P5 afterwards.  Link the copied P5 content to your P6 as an external runtime.