That's what hashes are for. First create a hash with the mac address as key and the hash pointer as value (the advantage is you need to do this only once):

my %macs;
foreach @aps {
  $macs{$_->{'ap_MAC'}}=$_;
}
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then your loop is reduced to this:

 $macs{"00:00:00:00:00:00"}{'serial'} = "FTX12345678";
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If you often need to know the array index too, you might store the index number as value into the hash instead of the pointer