No, no, no. You don't need to do that. I tried it by my own and You don't need to configure a File. I explain it a little bit more:
You start Zorin 16 on an USB-Stick in the Try-Mode. There You open a Terminal and type:
sudo cp -r /usr/share/backgrounds/zorin-mountain /home/zorin/Desktop/
Then You have the zorin-mountain Folder on the Desktop. Then you open on Z16 Nautilus. There You go on the left side to ''Other Places''. There You choose Your normal System that You use. You click on it and go trought the Folders till You come to Your Desktop. Then You move the zorin-mountain Folder to that Place.
So, now You have the zorin-mountain Folder in Your System. You can shutdown the Z16 Try-Mode and go back to Your normal System. There You should see the zorin-mountain Folder on Your Desktop.
Now comes the important Part: You must move the zorin-mountain Folder to usr/share/backgrounds because the xml-File in the Folder only works with this Path. So, You can move or copy the Folder graphically or You use the Terminal and type (the Command for copy):
sudo cp -r /home/[Your-User-Name]/Desktop/zorin-mountain /usr/share/backgrounds/
Then You should use Gnome Tweaks and change there Your Background Picture. But You must choose the xml-File. And then You have the dynamic Zorin Mountain on Zorin 17. To proof that it works, here a Screenshoot: