HAProxy-WI gives ability to change IPs and ports for backends servers on-fly without reloading or restarting HAProxy service. Just choose needs server, enter new IP, port and press the "Enter" button. Step-by-step how to is below.
Go to the Runtime API -> Change IP and port.
First step: we have to choose a server where we would like to change settings(in the black box)
Second step: choose needs backend(in the blue box)
Third step: choose certain server inside the backend, HAProxy-WI shows running settings, you have ability to change them(in the yellow box)
Fourth step: press "Enter"(in the red box)