No, you can't replace the seal without discharging and recharging the system. If it is still making cold when the clutch is engaged I just wouldn't worry about the leak. You might find that its easy to have A/C seem cold when its cold out though.
Deal with your electrical problem first. When you get back to the refrigeration system the oil level can not be determined and overfilling is worse than not enough. There are ways to make good guesses on oil quantity but that's better left to a professional. The only procedure I can recommend to refill oil after a repair is to flush the whole system and replace the installation quantity.
Bosch Master, ASE Master, L1
33 years MB technician