Resize Viewport on Macbook Air Because part of screen is broken
the short answer is no, there's no way to redo that in the OS so it assumes a smaller LCD.

the LCD Panels' I2C chip (IDED chipset) in the LCD panel tells the logic board (and firmware) what size display it is.  the OS responds by making settings accordingly.

The only option is to replace the display or have it repaired..