Older Mini changing nozzle size

I have one of the original Minis. I wanted more detail so I purchased the conversion head. I think the original nozzle was .5mm and the conversion head was .25mm.

So the question is with the conversion head can I change the nozzle back to .50 or better still .40 without putting the old original head back on?

And does Lulzbot sell the nozzles?