Absolutely, positively you can add one extension and run a Yezl Y3 with 2 cells (in series). See my pictures of the driver here: https://budgetlightforum.com/t/-/28129 - it clearly shows a nice big inductor: this means "buck". Definitely works with 2 cells, probably 3 cells, though I haven't tried that myself. I see no reason why it would not work -- look at the 3 cell option on the CNQ site. Should be the same driver.
For the HD2010 -- you will fry something - there's no inductor on a HD2010 driver, so cannot handle bucking down the voltage.