If you save something in the designer, regardless of what mode you’re in, if you exit and then restart the designer, it will load that last save. The staging mode just prevents a project in production from being altered, i.e. it doesn’t affect any clients running the project.
Like Josh said, you can clone the project before messing with anything by going into Config -> Projects in the gateway and making a copy. You’ll also notice on that same screen that there’s options for “export published” and “export staging” for projects that have staging and published versions of the same project. If you made some changes you don’t like, you can always revert to the export of the last published version of the project.
If you’re hinting at Ignition having a version control system, it doesn’t currently, but it is on our dev team’s radar: