AC Recharge - 1995 Regal

It looks as though the high pressure switch on the condenser line is bad.....there are signs of oil leakage and dirt that has stuck to the
tubing, where the oil has ran on to. The system has recently gone flat (this year) and a simple oil recharge has escaped as well. If I recharge the system now, can I replace the high pressure switch later, without the system losing the charge or will I loose the charge when I remove the high pressure switch?
Also, where can I add oil, since I am concerned that I may have lost oil when the system went flat. I hope I can easily add it to the system, without removing too many components.
Thanks, Joe
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