Since the PL command accepts a 32-bit value, is the permissible value for that command 0x00000000 to 0xFFFFFFFF?
Yes but note that the power level parameter is a signed value because it represents units in dBm (actually deci-dBm or dBm/10).
So for instance, to set a power level of -10 dBm one would write
FFFFFF9C (-100 in hex). If this parameter is used, the value FFFFFF9A is
read back since this is the closest value the radio could find to the