Have you tried using the igpu or another gpu for monitor the reflash with your original (or a working rom) with atiflash from the command prompt?
I haven't had this problem. But I plan to do this on a rig with 6 GPU. So yes it's easy to just change a normal GPU as "main" GPU. The problem is that one badly flash rom GPU may cause all system to fail
If the system fails you can try this: https://forum.ethereum.org/discussion/9443/bricked-your-rx-480-due-to-bad-flash
I flashed a 480 rom on a 470 and after bridging those pins during boot I was able to get it working again. Good luck!