I know that the Natures are not abusable, but my question is if they are decided at the same time as the IVs or not. If, for instance, the nature was decided when you picked up the egg and the IVs were decided before, one could play on an emulator and create a save state (or frozen state) at the correct frame/delay, then simply re-poen the state again and again until one got the right nature.
I don't know "when" the nature is created. I've been using only original cartridge games and doing it the hard way: get the delay, frame right, look at nature, restart if nature is wrong.