How to change the Text Wrap default in Pages
With Pages '09 (version 4.3 ¹):


Select a picture
Configure it completly as you wish
Define it as the default image style:

Format &gt; Advanced &gt; Define Default Image Style





With Pages 5 (version 5.5.1):


This function is missing.
The creation of an Image Style doesn't permit to save the Text Wrap tuning.



¹)  I removed my installation of Pages '11 due to its lack of functions. Its documentation isn't available on the Apple web server: Pages manuals.