To change the pointer, just open the TIFFs (called rfbCursor.tiff, rfbCursor2.tiff, and rfbCursor3.tiff) in your favourite image editor (like Photoshop Elements), and replace them with your own 16x16 TIFF images. In Photoshop Elements you have to select a checkbox in the "Save as" dialog to make it include the transparent background. Also, you will not be able to save directly into the COTvnc app. You have to save it to the desktop (or wherever) and then copy it into COTvnc afterwards.
My renditions (boring as they are) can be downloaded, if you'd like to save some time.

