What do you mean by lengthening receiver connecting wires? Do you mean from the battery or ESC to the receiver or to the individual servos from the receiver? In either case, make sure that the material and size are adequate for the current demands. If you do that, you can do fairly long extensions. They do make extensions for servos that you can simply insert between the servos and receiver in several lengths. An easy way (if you can solder) is to just cut the existing wires in two and solder in whatever length of wire you need. This is more reliable than the extension leads as the connectors (especially if hidden and not exercised often) will corrode and cause problems later on. In short, the answer is YES you can do this if you use the proper material and techniques.