The self made icons are only loaded from $OH_CONF/icons/classic.
I think what Michael is suggesting is you take advantage of Items | openHAB rather than overwriting the one icon.png over an over.
Your display Item’s state will consist of the combination of all the information you want to base the icon upon. Your dynamic icon generation code will create an appropriately named .png for that combination of states. As the display Item changes state the UIs will load the newly created icon.
I did something similar in Comprehensive Wunderground using HTTP Binding Example with the main difference being I just copy the icon instead of creating it from scratch.