Using a port that has a blown fuse or not, will pass on the single pixelnet universe that the hub is set for. the connected hub should be set for universe 1, even if the main hub is set for 3. This will have universe 3 on both hubs. The power and ground from the first hub will only be at the universe selection headers, and will not power the second hub.
Cutting the wires is a good idea, not really required.
This is not going to add power to the string, and you will blow the fuse if you put too many lights on the port.