Change default setting to ban a user

I'd like to change the default setting when I'm banning someone.
Now it's on default that the messages of the previous 24 hours will be automatically deleted.
But I'd like to change this to the option ''Don't delete any'' for evidence later on why someone was banned for. And to change the option every time is quite annoying to do that when you ban someone. Since I want to ban someone immediately and then I or a admin otherwise just forgets about that option.