An easy Karabiner Elements implementation for Colemak, its mods, and extend. Easy Colemak for MacOS!
Just go to the website https://profxwing.github.io/karabiner-colemak/ and everything should be taken care of.
Okay, a bit more in depth: First, install Karabiner Elements. Then, on the website, choose which mods (or lack of mods) you would like to add, as well as the extend layer. Next, press Install.
This should pop up with an install question, which you should confirm.
Now, in Karabiner Elements, just enable the layout (and extend if selected).
To enable/disable the layout, press LCMD + LSHIFT + grave (`).
Congratulations, you are now the proud owner of a Colemak layout.
For information about the Karabiner implementation, read https://github.com/ProfXwing/extend-karabiner For information about Extend in general, read https://dreymar.colemak.org/layers-extend.html
This script may only work when qwerty is set as the input source. The layout will likely work incorrectly if you use a different layout. Make an issue here if there's any problem with that and I'll come up with a solution for you. It's pretty easy to switch the original layout. It would be slightly difficult to implement every source layout, though.