At the present time, iScreensaver Designer 5.2 provides support for macOS 10.13 High Sierra, but there are some functional limitations.
Please read the 10.13 High Sierra Tech Note
as well as the Release Notes
Due to changes made by Apple, iScreensaver Designer version 5.2 does not currently support macOS 10.14 Mojave.
Please read our forum post
for the latest updates.
[Solved] Adding images to an installed screen saver?
Is it possible to add an image to the folder that I use for content and have an installed screen saver show it?
I will build the initial screen saver, but others want to modify the content, that the installed screen saver displays. It appears that only the licensed screensaver user can modify the contents and they have to create a new screensaver and install it. That appears to be the case and is a non starter for my application.