It might depend on what part of the robot you plan on using them on, whether or not they're allowed, read the rules carefully. But generally you can add connectors. It's pretty common for teams to use connectors on the wires from the speed controllers to the motors, for example, to allow quickly changing a motor or doing work on the transmissions.
The Anderson Power Pole connectors are popular for this
http://www.andersonpower.com/product...onnectors.html
They can be paired, in different orientations, and are available in several colors and sizes.