Search for your application in those directories and edit the files, using
root privileges where necessary.
sudo vim /usr/share/applications/org.gnome.Terminal.desktop
Now edit what you need, like the application command to add extra flags:
You can also add environment variables using
Exec=env LANG=en_GB.UTF-8 gnome-terminal --full-screen
Copy it to
~/.local/share/applications if you don’t want to edit the original.