Sorry, you can't change the shape of the health or power bars. You can change the vitals box around the actual bars, but not the green and blue bars themselves.
However, you can do pretty much whatever you want with the Attunement bar. All you have to do is edit images.
Here's one that made a few changes to the appearance:
http://www.lotrointerface.com/downlo...63-MilHUD.html
This attunement display (From Daimon UI) is completely different (In the top-right corner of the image):