If you keep adding electrons or protons to a Neutron star, what would happen? Are there decay processes that convert them to neutrons in the absence of the oppositely charged particle?
The pressures are so great in a neutron star that most of the electrons combine with protons and become neutrons. A statistical equilibrium is set up in which neutrons, because they are unstable, decay into electrons and protons while some electron proton pairs form neutrons. For typical neutron star temperature/pressures, at any one time about 1/7 of the nucleons are protons (with an equal number of electrons) and 6/7 are neutrons. If there were more electrons than protons, then the excess of electrons would persist since they would not have enough partners to combine with. Of course, this net charge would attract protons and other positive ions from nearby space and this would reduce the neutron star's charge. So, if you added electrons, you would change the charge of the neutron star, but the net charge would decay over time as positive particles are pulled in from space.