Hi Rasmus,

Yes it's possible by hooking into the BaseTree.BeforeNodeRender event.

using umbraco.cms.presentation.Trees;
using umbraco.cms.businesslogic.web;
using umbraco.BusinessLogic;

public class ChangeIcon : ApplicationBase
{
  public ChangeIcon()
  {
    BaseTree.BeforeNodeRender += new BaseTree.BeforeNodeRenderEventHandler(this.BaseTree_BeforeNodeRender);
  }

  private void BaseTree_BeforeNodeRender(ref XmlTree sender, ref XmlTreeNode node, EventArgs e)
  {
    if (node.NodeType == "content")
    {
      if (node.Icon = "icon.png") // quickest way of identifying a node type !
      {
        int nodeId;
        
        if (int.TryParse(node.NodeID, out nodeId))
        {
          // logic here to determine if you want to change the node icon....
          // to change the icon: node.Icon = "newIcon.png";
        }
      }
    }
  }
}

HTH,

Hendy