I have a CS cart licence - can I install on a second server to make changes and test results before making the same mods to my public site?
Yes you can. Just close the store and access the dev site through access key.
Yes, you can follow cs cart doc as https://docs.cs-cart.com/4.9.x/install/useful_info/copying_store_to_subdirectory.htmlto achieve what you want.
Great, thanks for the help
Adrian
How to close dev store-front for public you can find here
https://docs.cs-cart.com/4.9.x/user_guide/look_and_feel/changing_attributes/store_closed.html