You CAN do it yourself,
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This review is from: SE JT620 6-Inch Spring Bar Tool (Tools & Home Improvement)
I had a growing collection of watches that needed replacement bands so I thought I'd buy the tool and try changing them myself. I works! I can't say it was easy, exactly. It's a bit tricky to get things lined up properly and to use just the right amount of pressure (without stabbing yourself, like I did). It would probably be a good idea to buy an extra pin or two in case the original gets bent in the process. If you're all thumbs, let the jeweler do it.