Running Relay in parallel to switched neutral rocker switch
In this case you're looking at a relatively simple problem.  You want to switch a load with a simple existing control mechanism.  A switch controlling a load is a very simple circuit:







simulate this circuit &ndash; Schematic created using CircuitLab

Because you are trying to achieve function identical to the function of this switch, a relay in parallel to it with the right contact setting will bypass the switch and provide the same function.







simulate this circuit

With regards your question about a short, the purpose of a switch is to connect(short) and disconnect its contacts in a controlled manner.  Looking at the second diagram, you can see that with this arrangement, if either the rocker switch or the relay are actuated, the load will be connected to power.  Once the switch has connected, the voltage on both sides of the other switch will match, and actuating the other switch will have little consequence.

When choosing your relay, make sure it's controlled contacts are rated to do the same thing as the existing switch.  Match the current rating, voltage rating, AC or DC and any other relevant ratings and you should be fine.