We don't allow this for several good reasons, the most important being that it's imperative for us to control our own content. Allowing individuals to script their own unregulated content could get everyone in trouble, and we don't want that! If you have ideas for pranks, you can let us know, or you can try a prank call the good ole' fashion way :)
We do however offer the ability to customize pranks. Check for the green "Customize Prank" tag on pranks.
Were adding new customizations daily!