Torque wrench an option? If so, I imagine I need to find a spec in the owner's manual and then I can buy a torque wrench to match?
I change the blades on my mower every Spring (regardless of what amount of hours the mower shows).
Yes....good idea... "always" refer to the Owners/User Manual that is specific to your model mower first and foremost. The torque specification(s) is there just search for it.
First make sure you have the right size "socket" for those particular bolts/large nuts before you start (because you don't want to chance stripping/damaging the bolt/large nut!
Using a impact is the best for removing the bolt/large nut but if you don't have one you can always use a breaker bar, just make sure you secure the other blade(s) first before removing the bolt/large nut, when removing the old blade(s).
Definitely use a torque wrench and apply a bit of "anti-seize" to the threads prior, when installing the bolt back on with the new blade. Recommend to first use your hand to thread and tighten the bolt/large nut then apply the torque wrench.
Some may say that it really does not matter about applying torque, etc. but this is a very import feature that is often overlooked or ignored and could have damaging consequences later on, so keep that in mind.
Over all you can do it. It's an easy-peasy process, just take your time.
Just my $0.02