When may I change my transponder code to 1200 when being handled by ATC?
ATC will tell you something like, &quot;N1234R radar service terminated. Squawk VFR. Frequency change approved; good day&quot; which you will repeat back as an instruction.
You do not change from the assigned transponder code until instructed.
If you're in a hurry to get away from ATC, you may request to terminate radar service as soon as you are out of their regulatory airspace.