Hi all,
Is there a way to apply automatically custom per display scale in the plasma5 session on Xorg upon logging in ?
At the moment I issue following command in the terminal after login:
$ xrandr --output eDP-1-1 --scale 1.5x1.5 --output DP-1-1-1 --pos 2880x0 --fb 6720x2160 && systemctl --user restart plasma-plasmashell.service
I answered the question myself 
I achieved to run xrandr on plasma session startup before plasmashell is executed by adding ~/.config/systemd/user/plasma-plasmashell.service.d/override.conf with a content:
[Service]
ExecStartPre=/usr/bin/xrandr --output eDP-1-1 --scale 1.5x1.5 --output DP-1-1-1 --pos 2880x0 --primary --fb 6720x2160 --filter nearest
I also disabled kscreen backend service for the change to be effective.
xrandr -q gives what I wanted to.
So far I don’t see any negative side effects, beside kscreen is not running, obviously 
Maybe someone will find it useful.