Oso, tried this process and successfully downgraded with no problems to 1.8.0080. Then tried to downgrade to 1.7.0060 and got this:
========== 2014.01.01 00:02:44 remo-con disconnect======
Packet: P3X_FW_V01.11.0010.bin
Upgrading ...
Result: Success.
========== 2014.01.01 00:00:12 remo-con disconnect======
Packet: P3X_FW_V01.10.0090.bin
Upgrading ...
Result: Success.
========== 2017.05.16 14:25:19 =====================
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2017.05.16 14:28:05 =====================
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2017.05.16 14:31:46 =====================
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2017.05.16 14:39:38 =====================
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2017.05.16 19:28:53 =====================
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2017.05.16 20:03:34 =====================
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2014.01.01 00:00:12 remo-con disconnect======
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2017.05.17 05:12:22 =====================
Packet: P3X_FW_V01.10.0090.bin
Result: Abort.
The firmware on the SD card is identical to or older than the current firmware on the aircraft.
========== 2017.05.18 19:58:13 =====================
Packet: P3X_FW_V01.09.0060.bin
Upgrading ...
========== 2017.05.18 20:43:43 =====================
Packet: P3X_FW_V01.08.0080.bin
Upgrading ...
Result: Success.
========== 2014.01.01 00:00:14 remo-con disconnect======
Packet: P3X_FW_V01.07.0060.bin
Upgrading ...
========== 2014.01.01 00:00:13 remo-con disconnect======
Packet: P3X_FW_V01.07.0060.bin
Upgrading ...
Looks like it did not downgrade to 1.7.0060. Also now my RC firmware I think is at 1.6 (not really sure as can't get DJI GO app to tell me anything as it indicates not connected) and after trying to downgrade AC to 1.7.0060, now am unable to Link RC to AC using the manual Link process. IS this to be expected since I read in your post that RC FW 1.6 is only compatible with AC FW 1.8 or newer. I have tried to do the RC FW Manual method described in your post and when I hold down the tutorial button, I get a message that controller is not connected and does not offer any downgrades for it to download. Man, I have never had so much problems with FW. Prior to trying to downgrade AC FW to 1.7.0060, I was at least linking to the AC as both AC and RC lights were solid green and I was able to at least move the camera gimbal. But now, am not able to make the camera move at all as it now is not linked. I am almost ready to just send this thing in for repair. Thanks to all for trying. I really appreciate all the effort, but think I am at my wits end.