[other techniques]

Along with creating new circuit paths, as discussed, replacing components with others of a different style or value will also bend circuits in wonderful ways.

For example, a standard resistor on a circuit board can often be replaced by a potentiometer or photo cell (both are variable resistors). If this is a resistor that had set the pitch of a voice (very common), that voice now becomes tunable, changing frequency with the turn of a dial or the shifting of light. As would follow, a potentiometer can be replaced with a photo cell as well (i.e., the pitch dial/potentiometer of an oscillator could be replaced with a photo cell providing theremin-like, hands-in-space frequency control).

Motion sensors such as mercury, boxed ball, and "tilt" switches can be wired into small devices for dance or gesture-driven instruments.

Two solutions are at hand in addressing limited space for the mounting of  new controls. Circuitry can be completely removed from its original housing and installed in any number of new enclosures. Or, a remote control panel containing the new switches and dials can be constructed and run into the original housing by means of braided or ribbon cable, a type of self-contained color-coded multi-conductor wire.

In the instance of limited space to solder to, as in short component leads, IC pins, etc., study the circuit to see if the area you wish to solder to is connected to an easy-to-get-to trace on the board. This is often the case. A hard-to-get-to resistor lead within the circuit, for example, might connect with a printed-circuit trace that emerges, with full access, on the other side of the board. Soldering to a trace that connects to the desired component elsewhere is the same as soldering to the component lead itself. This technique can be a real tight-space problem-solver.