Here is an easy way to add your own customised icons to the Conditional Formatting feature.
1) Download the attache file "CustomIcons.jar.XXX" and remove the triple X file extension
2) Open the jar file with an archive tool such as WinRar and navigate to the resources folder
3) Replace the current 4 png files with your own (make sure they are named the same: 1.png, 2.png, 3.png, 4.png)
4) Paste the jar file in the folder <yellowfin home>\appserver\webapps\ROOT\WEB-INF\lib and restart Yellowfin
5) Then choose the Icon Set called "Custom Icons" and you'll see your new custom icons there.