No, there isn't. This software does not currently support modifying or adding a new rock pattern, you can only work with those that come pre-installed. What you can do is to export the current database you have (by clicking on File > Export Template) and edit it from there using another software that can view and edit Canvas External Tool File (.CVT), such as Canvas, it's really a good tool for making technical illustrations, it will work with both vector objects and raster images, and it is designed for easy using.
There are also more alternatives to the software you are currently using, such as Interactive Petrophysics that offers some advanced features and interpretation modules like: Monte Carlo simulation, that enables the user to understand and quantify the errors associated with a complete interpretation workflow or Rock Physics interpretation workflow.
