So the rebuild wasn’t bad, I followed the guide @cdsmith posted, and swapped the E0 pins with the E1 pins in pins_RAMBO.h, initially I thought it’d just be 3 numbers, but there were also the microstepper and digipot channels, so just search that file for E0 and make sure you switch them all.
If anyone else needs it and doesn’t want to go through the steps of building it: here’s 2.0.9.0.13 custom firmware to use E1 as E0. Taz 6 universal 2.0.9.0.13 extruder driver swap.hex - Google Drive
Just power down, pull the E0 connection and E1 connections, on the board. Leave E1 disconnected and plug E0 where E1 was, boot up the machine and load the custom firmware.