That’s what I’d like to use it for as well, but it’s difficult to do so because there’s no way to edit the disk image.

Any advice on how to create a JSLinux clone with a specific file pre-installed and auto-launching would be much appreciated!

Working with VMs always felt difficult because of this. So authoring was built-in to Docker. Now you can use Apptron to author and embed a Linux system on a web page. This aspect is usable, but it's only going to get better.