Methods for applying protective coatings to electronic devices that have already been assembled, and are in a consumer-ready or aftermarket form, are disclosed. In such a method, an electronic device may be at least partially disassembled to expose at least a portion of an interior of the electronic device. A protective coating is applied to some or all of the exposed surfaces of the electronic devices, including one or more internal surfaces, features or components of the electronic device. Thereafter, the electronic device may be reassembled. During and after reassembly, the protective coating resides internally within the electronic device. Systems for applying protective coatings to interior components of previously assembled electronic devices are also disclosed.