I understand that the LT1236 can act as a negative reference by controlling the voltage drop across an external resistor placed between the negative rail and the GND pin of the LT1236. If a trimpot is placed between LT1236's VOUT, TRIM and GND pins in the same way it would be when the LT1236 is used as a positive reference, does it perform the same trimming function? Or is there some other subtlety involved?
I don't have definite answer for now. I'll look into it further. But my assumption is that the circuit will work the same way. Trimming of negative shunt voltage reference can be seen in CMOS DAC with Low Drift Full-Scale Trimming circuit in page 9 of the datasheet.
I confirmed that using trim pin for negative voltage reference will be the same.