It's pretty simple to modify the memory straps of your original bios, which is a good start. All you need is atiflash and Polaris Bios Editor:

https://www.techpowerup.com/download/ati-atiflash/

https://github.com/caa82437/PolarisBiosEditor

Extract the Atiflash zip to a folder on your Desktop and open a command prompt in that folder. The first step is to backup your original bios in case something goes bad. At the command prompt type:


The above command assumes the index of video card you want to backup is 0. It's best to flash the cards one at a time and remove any other cards so you won't make a mistake. After you backup the bios, extract the Polaris bios editor zip to another folder on your Desktop and copy the bios you backed up to that folder. Run Polaris bios editor and open the bios in it. On the bottom right box, you will see the memory timing values. Most people start with copying the value in the 1500 or 1625 MHz box and replacing all the higher frequency values so they are the same. What works best is highly dependent on the type of card you have and the type of memory it uses, so you will have to research what works best for the cards you have. For example on my Asus RX 480 with Samsung memory, the 1750 strap works best.

Once you adjust the memory straps save the bios and copy it to the atiflash folder. Flash the bios to your card with:


After it finishes loading the bios, don't reboot as it asks you to. Since you are using a modified custom bios and the new AMD drivers since 16.12 check for a valid bios signature, you need to patch the driver or use a driver older than 16.12 for Windows to recognize the card. To patch the driver download atikmdag-patcher:

https://www.monitortests.com/forum/Thread-AMD-ATI-Pixel-Clock-Patcher

and use it to patch the driver before rebooting.