Will Seokai overwrite my existing meta tags, and can I undo changes?

Seokai only updates metadata when you choose to apply it, so nothing changes behind your back. Before any bulk update, it's worth creating a CSV backup of your current metadata, which Seokai makes easy.

If you ever want to go back, you can restore from a CSV meta backup. That gives you a safety net, so you can try new metadata without worrying about losing what you had.