HoodLoader2 VS CorsairLightingProtocol

The Mega2560 like the Uno has a second MCU that does the USB-Serial stuff, an atmega16u2. You can flash this one to show up as a USB HID device instead of serial through Hoodloader (https://github.com/NicoHood/HoodLoader2).

The library is compatible with all boards using the MCU ATmega32U4. This includes Arduino Leonardo, SparkFun Pro Micro, Arduino Micro, and Adafruit 32u4 AVR Boards. It also supports the Arduino Uno and Arduino Mega, but this requires the HoodLoader2 bootloader, see this wiki for more details.

hoodLoader2 might help you out. I've no experience with it though.

You should buy a Leonardo if you want to do USB projects, the Uno can do that stuff too - it has a small microcontroller (16u2) that's a cut down version of the one on the Leo (32u4) that handles the USB to serial conversion required for a PC to communicate with the main microcontroller (328P) on an Uno, the 16u2 can be reprogrammed to make the board appear to be anything - but it's harder to achieve for beginners. If you're interested in reading more, take a look at https://github.com/NicoHood/HoodLoader2, but if you just want to do keyboard and mouse stuff quickly with all "off the shelf" hardware and software (and the community support that entails) the Leo is definitely your best bet.

Though instead of paying for Corsair's stuff, it's possible to spoof it with an Arduino.

Or it's even possible to make your Arduino work as a Corsair Commander Pro using this (but you need to get one with a compatible chipset, like Pro Micro)

you can use this if you know a bit about electronics https://github.com/Legion2/CorsairLightingProtocol

The library is compatible with all boards using the MCU ATmega32U4. This includes Arduino Leonardo, SparkFun Pro Micro, Arduino Micro, and Adafruit 32u4 AVR Boards. It also supports the Arduino Uno and Arduino Mega, but this requires the HoodLoader2 bootloader, see this wiki for more details.

It's also worth noting you can make DIY Corsair controllers (can appear either as Corsair Node Pro or LS100 in both ICUE and SRGB) and they're pretty cheap with a microcontroller. I've done this successfully. Information on doing this can be seen here: https://github.com/Legion2/CorsairLightingProtocol https://github.com/Legion2/CorsairLightingProtocolBoards

RGB is controlled by an Arduino Beetle with CorsairLightingProtocol through openRGB. Which allows me to do funny RGB puke: https://youtu.be/ecw56ruBseo https://youtu.be/4Te-m9P7mEs

It seems like you got your questions answered but since I'm here and just as an FYI in case you might expand in the future. You can build a virtual lighting node pro out of an arduino board. IDK much about the details other than that people have already done most of the work for it. https://github.com/Legion2/CorsairLightingProtocol But I imagine it'll be the cheapest or easiest rout since you can get arduino for only a few bucks. I wish I had more knowledge about arduino. I'm thinking of making a DIY nanoleaf equivalent and if I run it off ICUE I'm stuck with its too small of a LED limit. Those ceiling strips are ICUE's max of 138 LED and stretching out 5v that long gives me power drop issues. I can only get away without having to add power injection because the static blue is set to only 16% opacity in ICUE so the full power blue wave can be seen well traveling over it.