[wakedb]

if you run server as casual mode: game_type 0; game_mode 0 cs:go use Valve's game mode settings: gamemode_casual.cfg If you want make changes to Valve's settings, you use override file, which is: gamemode_casual_server.cfg

Well, that's exactly what I did. I'm not sure what you're trying to explain to me.
I'm running a CS:GO server with game_type 0 and game_mode 0, so it casual. I put that extension _hns to my gamemode_casual_ so I know that's the one I need when I want to change anything in there.

In CSGO, to override Valve's game mode setting, you use override config files. For example ...cfg/gamemode_casual_server.cfg

I do change settings in gamemode_casual_myserver.cfg instead of gamemode_casual.cfg cause I know it overrides it.
As I said - hns comes from Hide N Seek. That's the name of the main plugin on my server. My server has to run a gamemode which is casual. I never change anything that can be found gamemode_server.txt.