I used studio 6 to save a .hex sketch from a working Jeenode. I would like to convert that to .ino , has anyone done that already?
think it is not possible.
Whilst decompiling is technically possible, you wouldn't get anything back that resembled the original IDE source code.
So, as far as your specific question goes, no it's not possible.
It's kind of like baking a cake.
Can you take a cake and convert it back into it's raw ingredients? No. But you can take it to a lab and have it analyzed for nutritional content. That's like disassembling. You get back something much more fundamental than the source code - a human readable representation of the machine code.