Put that file in your Houdini preference folder to automatically make the display/render flag follow your new connections (houdiniXX.X\scripts\onInputChanged.py)

onInputChanged.py

def automatic_display_flag(node, index):
    """When connecting input, this script will change the display flag is the input connected has the display flag on"""
    try:
        if node.input(index):
            if node.input(index).isDisplayFlagSet():
                node.setDisplayFlag(True)
            if node.input(index).isRenderFlagSet():
                node.setRenderFlag(True)
    except Exception:
        pass


automatic_display_flag(kwargs["node"], kwargs["input_index"])