If you want to create keyboard layouts, keyd
is very good for that. You can create several keyboard layers and use whatever key you want as a modifier.
I use it to mimic the windows “US International with dead keys” layout that I’ve grown used to but it can do so much more.
I know it has been a while, but thanks for posting this. I really missed the deck tracking and statistics. The overlay is broken but tracking seems to work. Thanks for this.