Backup-TA I'm confused

I have a Z5 E6633. I've read that I should back up my TA partition before I unlock the boot-loader. The Backup-Ta programme says that it needs root. To get root I need to unlock the boot-loader. If I've unlocked the boot-loader it's too late to backup the TA partition isn't it? Or am I missing something here?

Can somebody clarify this?

Thank you.

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