I have the ROG Harpe Ace Aim Lab edition mouse and just got the ROG Strix Scope II 96% wireless keyboard, both support the ROG Omni Receiver and I wanted to share how easy it is to upgrade. Here is a more detailed guide you can follow, but I'll list it in steps as more of a quick start guide.
3) After updating, you should see the ROG Omni Receiver in the Armoury Crate Device list.
4) Update the ROG Strix Scope II 96% wireless keyboard with Armoury Crate.
5) On the ROG Omni Receiver page, under "Paired Device", if any are paired, click the X in each box to unpair them.
6) At the bottom under "Add Pairing Device", click Mouse, hold the pair button for 3 seconds, it will give you a message it was successfully paired.
7) Click Keyboard, Press and hold the Fn+7 key for 3 seconds, it will give you a message it was successfully paired.
And that's it, you should see both devices paired under "Paired Device". I paired them to the ROG Strix Scope II 96% keyboard's wireless dongle, since I no longer need the ROG Harpe Ace wireless dongle, I put it in its place under the mouse to not lose it.