@gemlog Can't you do that with normal compose key magic? 🤔
Then there's wtype — as the name implies, it just "types" any character (or string of them) you want.
I have two dead keys on one of my computers and I just bound two unused ones to a short script that uses wtype to output the required letter depending on current layout (I parse the json output of "swaymsg -t get_inputs input" to figure that out).