A bootable pendrive made non-bootable? Sure, just remove the operating system or boot files. In most cases, though, since you’re blindly writing an image to the pendrive, you’d probably be better off saving the files you want to another device, then formatting the pendrive. (There are other ways to make a pendrive bootable and, if you understand what you’re doing, you can undo just the boot part.)
However, if the USB drive comes before the hard drive in the computer’s boot order, some computers may just fail on the pendrive’s inability to boot, rather than bypassing it and trying to boot from the next device in the boot order.
What I would suggest is uninstall and create a new live USB using etcher. I found this website helpful: https://etcherpc.com/