Techspray offers the TraceTech Conformal Coating Remover Pen that allows you to remove a tight area of coating around a repair area without affecting the rest of the PCB. You first saturate the tip by tapping it lightly on a surface, which opens the valve and releases solvent. Holding the tip down may oversaturate it, which could lead to solvent flowing into unintended areas.
No, conformal coatings are non-conductive, or insulative. The job of conformal coating is to isolate the PCB or components from the environment and even components (i.e. high voltage or high heat) from the rest of the board. To do that properly, a coating must have electrically insulating properties with as high of a dielectric withstand voltage (or strength) as possible.
While conformal coatings can offer a moisture resistant layer of protection, most cannot be considered waterproof. Even if applied heavily, most coatings are semi-permeable, so allow some amount of moisture through. Conformal coating can, however, prevent current leakage or corrosion due to ambient moisture. To truly waterproof electronics, you either need gasketing to seal the electronics within the packaging or cover the electronics with a waterproof encapsulant or potting compound.
Whether or not conformal coating is required depends on the environment the electronic device will operate in, the reliability requirement of the device, and the cost of failure, whether in dollars or human lives. Typical consumer devices are generally not coated because cost is one of the top driving factors, and a coating step certainly adds to that. Devices operating in harsh environments may require coating, and the type of stresses and contamination will point to the best option, whether that is acrylic resin (AR), silicone resin (SR), urethane resin (UR), or some other type of protection. Aviation, aerospace, and medical devices often require coating because of the mission critical nature of these applications.