When you are renovating or rehabilitating a house, the electrical demands of the house will change, which may mean major changes to key parts of your electrical circuit. It is advisable to use a professional, as many considerations will need to be taken into account on a case by case basis.
The first thing to think about is the change in total electrical load when the renovations are finished. With most renovations, the increase in load will usually be enough to need to change the size of the circuit breaker box, which requires a professional. This is because the size of the box is normally determined when the building is designed, and it is calculated for the original power demands of the building.
If you are demolishing one side of a section of wall or ceiling, you could uncover nearly anything in terms of electrical wiring. If you feel overwhelmed by what you find, that is a sure sign you should consult a professional.