You wrote in the description of setAuthorStyle() method:
"Caution, if widget attribute are already cached, you need to call the invalidateStylePropertiesCache(propagateToChildern)"
But calling invalidateStylePropertiesCache() is not enough, clearCachedStyle() should be called also to make getStyles() reload cachedStyles using Kuix.getStyles(this) which in turns calls widget.getAuthorStyle(), and the last one will apply the new AuthorStyle set by setAuthorStyle() method.