You cannot truly disable the ‘New’ button per se however, you can change the functionality so that it does not have the function of creating a new file. You can change it so that when you hit the button it will start recording instead of creating a new file. This will also give the slide switch additional functionality.
Go to the file menu and choose ‘Device’ > ‘Programmable Buttons’.
To the right hand side you will see ‘New and Slide Switch functions’ Choose Type B or Type C to change the new switch to ‘Record’. Note: There will be changes to you slide switch functionality when you make this choice. When finished, hit the update button to apply changes.