To edit DOSBox configuration in contrast to Windows, just we need to type the next lines on terminal to open the DOSBox\ [version]\ Preferences

cd ~/ 
sudo su
cd /Library/Preferences/
open DOSBox\ [version]\ Preferences

First we go to our user profile folder with ~/ and then we change here to super user, to finally go to Preferences folder to open configuration file for DOSBox [version]

After writing the lines above, the system will open a file like the following

NOTE: save the file to see the changes