I found that I needed to replace all the guids in a file with new ones. So I prepared for a miserable afternoon of cutting, pasting and developing RSI.

Not really, I wrote one line of powershell script:

(get-content C:\in.txt) | foreach-object {$_ -replace ".{8}-.{4}-.{4}-.{4}-.{12}", [GUID]::NewGuid().ToString("d")} | set-content C:\out.txt

I'm starting to see what all the fuss is about.