Hubble has three flywheels, each for x, y and z axes. By speeding up or slowing down a wheel they can rotate Hubble around that axis. The problem is, if there are minute forces on the craft, eventually one of the wheels will get to its maximum operating speed. There is no way to slow it down without putting Hubble into a spin in the opposite direction. Normally they will use a thruster to push against the wheel so they can reduce its rpms. Hubble has no thrusters. It does have some loops of wire it can energize to push against Earth's magnetic field.
If you take energy from solar cells and inject it into a tether it can push against the Earth's magnetic field and raise the satellite.
If you pass the tether through the Earth's magnetic field and extract electicity from it you can drop the satellite down.
It is not desirable to allow a spacecraft to develop a net charge. It floats everything above ground and plays havoc with measurements. Many steps are taked to control charge and get rid of it. They don't need to use it to make electricity, they have plenty of that from the solar cells which basically recycle the same electrons over and over again.