How to change icons in Google Maps clusters?

Question

Google Maps

The Google Maps documentation clearly describes how to work with label clusters, but it is completely unclear if there is a way to change cluster icons after they have been created?
Our task is to show part of the clusters in the "warning" state, change their color to red, and this state can change at runtime. Does anyone have similar experience? Googling, smoking documentation and stackoverflow so far have not led to anything.