well you gotta love Shimano, at least they have documentation with exploded drawings.

I don't care for the one shot threaded barrel nuts that are of indeterminant size and threading.

the comparable Campagnolo hub retains the freehub body with 3 set screws. Much easier.

If the impact didn't budge it you either were turning the wrong way - or you were just holding the wheel and the force of the impact was not being transferred into the part.

I think if you clamp the tool (12 or 14 mm allen) in a vise and use the wheel as your leverage you might get it.. pretty sure the barrel nut will be convention RH threads (lefty loosey).

or just build a new wheel

/markp