No, it's generated by the internal bluetooth stack. By the way it is 6 digits, not 4. You shouldn't change it anyway since it should be a randomly generated code. The standard says:
If the IO capabilities of a device are DisplayOnly or if Table 2.8
defines that the device displays the passkey, then that device shall
display a randomly generated passkey value between 000,000 and
999,999.
If you don't need a code you should use the "Just Works" pairing method.
Why would you like to change the code?
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