Karabiner is definitely degraded with Sierra
<https://pqrs.org/osx/karabiner>
From the Karabiner web site:
macOS Sierra support status
Karabiner does not work on macOS Sierra at the moment.
We are developing Karabiner-Elements which provides simple key modification for macOS Sierra at first. (Karabiner-Elements works well on macOS Sierra. We are working on fixing several remaining issues.)
We'll start updating for the full featured Karabiner for Sierra after Karabiner-Elements is completed.
https://github.com/tekezo/Karabiner-Elements/blob/master/README.md
I use Karabiner extensively on my work iMac, and at the moment it is running El Capitan.
On my Sierra Macbook Pro I've been using BetterTouchTool for my hotkey mapping. I like, it but there are some things only Karabiner was able to do for me, so my work iMac is staying at El Capitan until Karabiner catches up to Sierra, or I have to upgrade, and then I'll adapt.
Speaking of BetterTouchTool, it has features for mapping mouse buttons
<https://www.boastr.net/>
I will note, that I used to use a 9 button Logitech mouse years ago, but once Apple release the Magic Trackpad, I had mine 2 days, and that was the last time I used the Logitech mouse. BetterTouchTool and the Magic Trackpad gave me more functionality and custom gestures than I could configure into the 9 button mouse.
I will note, that there are other mouse drivers out there that can be used to provide button mapping. I was actually using one before I switched to the Magic Trackpad. SteerMouse was one, Mouse Wrangler was another (I think, as it has been a lot of years since I switched to the Magic Trackpad)
