Can you slow Earth's rotation artificially?

Not so that it made any difference. I just read a New York Times article that says that humans have made a measurable change in the rotation period of the Earth by several microseconds just by damming up all the fresh water into vast reservoirs containing trillions of tons of water. This has happened mostly in the equatorial temperate zone where humans mostly live, and dynamically, this is just where you would want to move mass to have the greatest effect. There may be a weak interaction between this activity and the weather over the long term, and perhaps even in the strength of the Earth's magnetic field which may be very sensitive to the rotation rate of the Earth.