You can do that without setting up a repository. But now-a-days you have to leverage an API.
Back when you had the old Rhino based editor you could export a stand-alone project as a JSON file or import a stand-alone project from a JSON file. The downside was that back then we could not import/export the scripts of a container-bound script (the feature was only applicable to stand-alone scripts).
You can still export a standalone GAS project from the Google Drive GUI and get a JSON file. But you'll have to use the Google Drive API to import it back into a project. Here' some documentation for that:
https://developers.google.com/apps-script/guides/import-exportThis method of importing/exporting standalone GAS projects via the Google Drive API is probably deprecated, since you won't find links to this information from the main documentation anymore. So use it with the understanding that support for this method could disappear without warning.
The modern way to do things is to leverage the Apps Script API, that is what CLASP uses under the hood. You can use it directly yourself without CLASP or setting up a repo. Plus it works for both container-bound and stand-alone scripts. Documentation for the API is linked below:
https://developers.google.com/apps-script/api/reference/rest