Blog Labels

A question for all you bloggers. What do you do when you want to create new labels that would apply to lots of old posts? I was thinking when I wrote my last post that I should have "etsy" as one of my labels because I often post about etsy finds. Do I just apply the label to relevant posts from now on, or should I go back through all my previous posts and add the label? That sounds like such a chore and a bore! What do you do?

OK, so I'm just about to post this and realise that I don't have an appropriate label! Maybe "help me" might be a good one...