So here's another script I just wrote. Spent a couple of hours on it only to find that there is a script called Reposition Anchor Point by Charles Bordenave who runs nabscripts.com. Its also available for download at aescripts.com. I decided to post mine anyways because it does handle things a little bit differently.
The point of move anchor point is to change the placement of the anchor point of the layer without changing the position of the layer. The script quickly move the anchor point to one of nine key places on the layer, (shown in the image above). If there are keyframes on the anchor point, position is not maintained, but a new anchor point keyframe is set to the desired position. If there are position keyframes, the anchor point is moved and position is corrected for all of those keyframes. This means that any position animation that you have already set up will not be changed by the script. (That is where it differs from Mr. Bordenave's script)
If you have any suggestions for making this script better or experience any problems, post them here or send me an email.
By the way, I went through this script file and made a bunch of comments explaining the entire script. So if you are just starting to learn scripting or are just interested to see whats going on inside, feel free to check it out.