Hello Mark,
The intended place for any UI technology is method DETERMINE_SPOT_ICONS of the control adapter. The default impl. resides in class CL_VBI_CONTROL_ADAPTER_GEO. There are two options for changing the icons:
1. derive your own control adapter impl. and overwrite this method
2. If the default pin assignment is sufficient you may simply replace the images. To do so provide an alternative MIME repository path to method GET_INITIAL_ZIP_ARCHIVE of class CL_VBI_GEOMAP_APPLICATION
In the later case all pin images need to be available under the new path.
Hope the answer your question.
Cheers Uwe