I have a 2006 JD 2305 with a 54" mulching deck. I have been removing and installing the blades with a impact wrench for 11 years, no problem.
Yesterday, after sharpening the blades, I was hammering the bolts as usual and stripped them out. I guess after 11 years, they just couldn't take it anymore. I guess that's why the manual says to torque them down to 50 ft.lbs.
Well instead of spending $72.00 each for new spindles, I retapped each one with a 1/2 x 20 tap.
Worked out great and saved me some money.
Long story short, go easy on the impact wrench.