How to save half-made service in Automator?
It does not matter if it's unfinished. Doing Command+S will save it under ~/Library/Services.

Taking the Service out of ~/Library/Services and restarting Finder (if you want immediate effect) will make this Service not to be shown under Menu / Services. Putting it back will, of course, make it appear again.

It does not matter where the file is placed, you'll be able to open it with Automator to continue editing it.