IO540, I didn't quite understand the original question. Certainly at a 'proper' international airport you do not need to clear customs for just a refuel. I suspect (but this is a guess) the answer is in your second post -
A Customs airport has an "airside" (at least, during its Customs hours)
and a 'customs by PPR' airport probably does not have an 'airside' unless the PPR has been applied for.
If I understand the scenario - you are planning to land in a country which would require customs clearance if you were to go landside, the airport is Customs by say 12 hrs PPR, No customs notification has been made as you don't plan to clear customs as it is only a technical stop, the airport refuses your landing.
From the State's perspective I can see that they could deem the airport to be a Customs airport only if the PPR process has been complied with. I can also imagine that this facility is designed for arrivals only, not transits. Certainly this is true in the UK, where you can not treat a concession aerodrome as an international aerodrome for anything other than a normal GA arrival or departure.