If I have my already carbonated kegs set at serving pressure for an extended period of time, do I have to worry about them absorbing more CO2 and becoming over carbonated
No, they'll reach a certain saturation level at any given pressure. There are alot of keggers that will pressurize their beer to 30 PSI for a fast carbonation for a few days and then dial it back to 10 psi for serving levels.