Both of these are already supported.
The first feature is governed by "File" -> "Preferences", tab "Display", option "Paint Nodes over Edges".
In the case of diagrams with group nodes, the grouping hierarchy might prevent the strict adherence to the chosen rendering order policy, though. I.e. if "Paint Nodes over Edges" is enabled and a top-level node is connected to a node belonging to a group node, then the group node will be rendered below the edge.
No matter which policy you choose, edge are clipped on the border of their source and target node, though. I.e. there is currently no way to have edge endpoints rendered above the corresponding source or target node.
The second feature is available through a label's "Icon Properties" property. I.e. select a node or an edge with a label, then go to the properties view in yEd's lower right corner and click into the value field of property "Icon Properties" in section "Label" to open a dialog which offers a means for importing an image to be displayed in the label. If you directly select a label, "Icon Properties" is available in the "General" section in the properties view.