How to use 350mA constant current driver with a 180mA LED
Can anyone see any problem with putting a resistor in parallel with the LED to drop the current from 350mA down to the recommended 180mA? 


yes. That won't work out, or at least, it's hazardous.

Diodes, unlike resistors, reduce their effective resistance when heating up. Thus, after initial "correct" setting, the current through the diode will increase, due to the temperature increase and the resistance decrease.

That, in turn, means the diode gets hotter. And then, its resistance reduces, further increasing the current through it…

A vicious circle, often called thermal runaway. It usually ends with the diode failing by burning out.

One thing you could do is have another constant current source feeding the diode, and a "waste power" resistor in parallel to that. But it's an ugly solution that's not going to be easier than ripping out the original CC source.