It doesn't change anything.... I was simply explaining the design characteristics of the F-5 Airframe not it's overall capability.....
In terms of design the F-5 Airframe is an extraordinary overall design! People keep asking why didn't they change the design and the fact is there is nothing wrong with the design! And until Iran builds a militarily sound powerplant with far greater thrust that can carry a greater number of weapons then militarily there is no reason to make any major changes in design.
As for small changes sure they could of made small changes like changing the back design of the Tailron and stabilizer... but those are mostly cosmetic changes and militarily these is a good reason why you wouldn't want your enemy to be able to distinguish between an F-5E and a Kowsar when their radars are off which is a far more practical reason than cosmetic changes...
But anything major like putting the wing on top of the Air intakes would of required Iran to build much heavier landing gears....
or
Adding an additional stabilizer would of increased drag, weight & weight balance that would have no doubt effected it's speed and that added weight would also effect your payload capacity which F-5's are already short on due to their weak engines....