Is it possible to download the demo site after the original installation?

Well, I didn’t download the demo site when I installed MODx, and now I see that that was a really bad choice!
Can I download it somehow without losing all the pages I have already made in MODx manager?

Hi.
I guess it’s a matter of taste to call that a "really bad choice"
I prefer to not install the demo myself, although it could be useful for learning purposes. If i were you i wouldn’t try to merge your current content with the demo content. I’d rather create another modx installation in another folder, using a second Database or if that’s not an option, use another DB Table Prefix (eg. modx_demo_).

Edit:
Using a second installation you can mess around with the demo without the risk of breaking your current website. It’s always a good idea to have some sort of "MODx Playground" where you can test various snippets and configurations. I prefer to have this sort of installation on a local machine, not on a public webserver (to avoid the risk of security holes or similar).