I've got a situation where a server being used as a DP (among other things) is being replaced with new hardware that will have the same name - I realise this isn't ideal but it's out of my control.

What I need to do is ensure all content that is currently located on the existing DP is transferred to the new server. Can anyone guide me through how I would achieve this?

I believe you will have to retire the old DP gracefully (removing all the content) and re-distribute to the new one.

You could create prestaged content files (.pkgx) if you don't want to copy all the packages over the WAN/LAN again.