'Customizing' pins_arduino.h file

I’m using a Sunfounder atMega2560, Sunfounder Ethernet Shield, and a TinySine RS232/RS485-TTL Shield for my project. The TinySine offers a “UART - Soft Serial” switch that can either connect Pins 0 & 1 or Pins 2 & 3 to the RS232 or RS485 connection (depending on that switch placement). My preference is for a ‘clean’ look without patch wires running from Pins 18 & 19 on the Mega to Pins 2 & 3 on the RS232 Shield.
I would like to be able to utilize Pins 2 & 3 as Serial1 in my program and place PWM2 & PWM3 to Pins 18 & 19 (since I’ll never use them).

Has anyone modified this file before and defined your own pin layout? If so, what exactly gets changed so someone doesn’t brick their card?

Thanks

pins_arduino.h (13.4 KB)