Take over/fork this project - https://github.com/Swoogan/Octopus-Cmdlets
These Cmdlets are a HUGE timesaver since you can't (as far as I know) create a copy/clone of a variable set.
The module does a lot more though, however the latest binary from 2015 doesn't work anymore and the developer doesn't appear to be keeping the code up to date.
Peter Bollwerk commented
I meant that you can't create a copy/clone of a variable set using the UI, as far as I can tell.
However, with these cmdlets, you were able to export a variable set to an XML file, edit it as needed, then re-import that XML and populate a new variable set with the values.