I may try leaving a spring compressed in a vice over night to see if that causes said spring to have less recoil?(is the the correct word there?)...if not I'll borrow the wifes 14" bolt cutters.
I have two of the Mag 2-D lights for modding, for use with 2x26650 cells. One is for bi-pin bulbs, and other for ROP bulbs. I realize that I'm not going to get maximum output from the ROP bulbs on 2 Li-ion cells, but I think I'm through with 6xAA adapters.
I got a shortened tailspring for one of them from Kaidomain, and it is
still a PITA to get the tailcap on. It's possible, but I was worried the entire time about screwing up the threads. I ended up taking a file and smoothing the spring's point of contact with the 26650 cell, because the end of the spring had sharp edges and I didn't like how it was so aggressively scratching/furrowing the end of the cell. I may end up getting another "shorty" tailcap spring from Kaidomain. It was only about $4.50, and I think the shipping was free. I would probably try shortening this one even more, then creating a new "circle" on the end, and bending it about an inch in, at a 90 degree angle.
If you had thick copper wire, and could find something the perfect diameter to start with for "wrapping", and could find a way to taper it, someone more skilled than I could probably make their own.