1.
you could probably use automator to do the job
or
2.
you can use xnview a free browser with editing features:
XnView
in versioin 1.91 (current version is 1.92) you cannot select a folder and change IPTC data off all images in there BUT you can select any number of images and change their IPTC data in a single operation.
to do that you can either right-click and select the IPTC data option from the context menu or you can find it as a sub-option under metadata in the application menus.