User TonybonJoby in our own forums has successfully flashed his XFX RX 480 graphics card with the BIOS from a Sapphire RX 580 Limited Edition (the one that runs at 1411 MHz Boost clocks, yes.) Having obtained the Sapphire's BIOS right here on TPU, he then flashed it onto his graphics card (which possesses a dual-BIOS setup; this is an important point which you should consider, as it gives you an extra safety net should anything go wrong) through ATIFlash. The newly-christened RX 580 thus smiles for the screenshot, with a stock clock of 1411 MHz, higher than most overclocks possible with the RX 480 cards, probably due to increased voltages on the BIOS level. The user then tested the card on The Witcher 3 and Furmark, with no problems having been reported. Just remember to back-up your BIOS with GPU-Z and make sure to peruse our forums for some details on this flashing process before you get the proverbial grease on your elbows.
Essentially, this may allow you to bypass some artificial overclocking limitation with your graphics card, probably by increased voltages on different power states of the card. You should do this at your own risk, and remember, the only guaranteed way of getting an RX 580 is... you guessed it, buying an RX 580. However, this might also give you an extra performance boost, and free performance is always good, right?