Can I recuperate a recording I accidentally saved as a webarchive?

What kind of recording was it that got altered? Was it a screen recording?

– Oh, and you can restore the file suffix back to .webarchive since that trick didn't work. –

Yes, all Mac computers come with the Time Machine app built in. To use it requires that you have an external drive that you can connect to the Mac as a location for TM to store its backup files. This is only one way to backup your Mac, there are others. But with TM you can restore deleted or altered files and you can restore your Mac to working in short order when something goes wrong and if you have kept the backup current. Backing up your computer is a must.

Please see: Back up your Mac with Time Machine - Apple Support

How did you accidentally save it as a webarchive?

Try changing the file suffix from .webarchive to .mov.

Do you have a Time Machine backup? Restore the file from that.