A user named TonybonJoby from TechPowerUpforums has successfully flashed his XFX RX 480 graphics card with the BIOS from a Sapphire RX 580 Limited Edition.
The Sapphire RX 580 Limited Edition features a 1411 MHz Boost clock speeds, and the BIOS is available on the TPU forums here. TonybonJoby has flashed this BIOS using ATIFlash onto his RX 480 card which features a dual-BIOS setup; (which is an important point that you should consider, as it gives you an extra safety net if something goes wrong).
As you can see the flashed RX 480, trend into RX 580 featuring 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.
TonybonJoby has tested the card on The Witcher 3 and Furmark, with no problems having been reported. Just remember to backup your BIOS with GPU-Z and check TechPowerUp forums for details of this flashing process before you try to do the same with your RX 480. Though there is a risk involve with flashing BIOS, and you should do this at your own risk, there is no guaranteed that it will work with every RX 480.
It also raises some question about AMD’s claims of improvements and indicating of a simple rebrand of old GPUs with new BIOS.