i have not had any success unlocking the mobile rx560 mxm cards. i have tried cross flashing but that got me no where either. i do believe it can be unlocked but it requires a specific bios to get it done. its really a hunch that i have but i do not have the time to dissect an AIO pc bios and create the necessary file.
after you flash the bios reboot the pc. then use
amd/ati pixel clock patcher to patch the drivers and reboot again. if the display drivers are not working still than go to device manager and under display adapters right click the graphics adapter and press disable then re enable it.
also, the card may not unlock but the bios should still flash. i bumped the memory up from 1500mhz to 1750mhz. also bumped the core clock up. if the unlock is not successful you will get a bit of performance increase from the increased clocks. more than you would have from the unlock alone. please post a gpuz screenshot of the new bios.
good luck.