Nah, it's the same directory structure. You just have to find where "packages" is. If you downloaded the assaultcube tar.gz, you should know where it is. If you installed it with a package manager, it is probably in /usr/share/assaultcube/ or ~/.assaultcube_something/. Or both. You shouldn't actually really change anything in /usr/share/assaultcube as it'll just get overwritten when you upgrade.
If you're really stuck try "sudo find / -name scope.png".
If you're really stuck try "sudo find / -name scope.png".