That is a good question. For the majority of Deepin users all they need to do is open the Deepin Control Center and go to Dispay and  Resolution settings and they are saved in ~/.config/deepin_monitors.json Though this file does not seem to change anything if you modify it. The only way I know of is to write a xrandr script for a special permanent setting if your using open source drivers.

So far so good but with the setup of the X server in Deepin it is not fully clear where to put the line to trigger the xranr srcipt

My preferred location was to use a text editor to create a file containing a xrandr script in      ~./xprofile
I do not currently use a script in 15.2

I know deepin uses wayland