I have a Kingston flash drive and I want to install Tails. But I read somewhere that when you install an OS on a Kingston flash drive, it can't be changed back to a regular flash drive. If I install tails, would I be able to format that flash drive to what it was, or it is permanent? Or do I need to have a USB stick just for Tails?
Installing tails does not destroy your usb stick.
The tails documentation explains how to uninstall tails from your usb stick, see this link:
It has instructions for Windows, Linux and Mac.