Years ago works on a Ferris mower that had the same type of bolt all the way through the spindle with nut on top. Could put the nut on finger tight, and when it would come in 3-4 weeks later for blade sharpening it would take a 1600 ft/lb 1" impact to remove the nut. the 3/4" 900 ft/lb wouldn't budge them.
Use grade 8 bolts with antiseize compound on threads & a torque wrench & you should not have any more problems.
I don't change blades often, but I have had a problem getting the nuts loose even with a 600 FTLB impact wrench. I installed a flat washer under each nut and I haven't had the problem since. However I do have to replace the flat washers periodically. The cordless impact tool will have an unknown torque output and the state of charge and battery condition will affect the torque output. I don't recommend using anti-seize on the nut as this can easily promote an over torque condition. I'm not sure why you change blades daily, but I have no idea what type of mowing conditions that you have to deal with. At the end of your work week you must have one large pile of blades to sharpen!!!:confused2:
Gees, I wish I could get you to talk some sense into some of my customers. They ask me about sharpening when the cutting edge is about 1/2 the blade thickness then complain when I tell them they need a new blade. After fitting I get "runs like new & cuts so much better" but when i suggest regular blade changes I might as well be speaking in Swahili.