safarisoftware-recommendation
I understand a Safari webarchive is a single file with the source code and other resources from a web page concatenated into a single file. I found a Macworld article from 2006 describing a program that does just this, but the link to the program is no longer current.
Is there any currently available software that can convert a Safari webarchive file into a more standard format?
You can remove the bundle document type for the .download extension.
You'll have to edit /Applications/Safari.app/Contents/Info.plist and remove the entry for the download extension under Document Types. The only disadvantage to this is that, whenever Safari updates, you'll have to do this again as your changes will be overridden.
I'd also make sure you make a backup of the Info.plist file first, before you make changes, incase you move the wrong line(s) or Safari gives you any issues after making the changes.
To answer the question about Saving in Safari:
When you are about to save a page you are viewing in Safari, you will find a Select option in the saving dialogue, that will let you choose the format you want to save the page.
By default it will be set as Web Archive. But you can change it to Page Source, so it will save on the source of the page, which in the csv case, it will save the csv file.
Next time, Safari will remember your last choice.
Best Answer
WebArchiveExtractor
I recommend WebArchiveExtractor. You can drag .webarchive files to this app which will extract the file into its individual files in a folder.
You can customise the output in Preferences, including setting a custom index file name:
WebArchiveExtractor is open source on GitHub