Feasibility of replacing cracked AC condenser fan blades
This type of failure is fairly common, and usually doesn't cause too much collateral damage, if caught quickly.
If you want to attempt the work yourself, it is fairly straightforward as you describe. You'll likely have to source the replacement blade from a local HVAC company, or the internet. You'll also have to balance the blade, so that it doesn't destroy itself again.
Once you open the unit, you'll want to inspect it closely for damage. Specifically, look for deep cuts and dents in the coil. There may be  some superficial damage to the fins, which likely isn't too big of a deal. If there's  lots of damage to the fins, or damage severe enough to penetrate the refrigerant lines. You will need to repair or replace the coil.
Also look for damaged wiring, as that could require replacement of the motor.
When purchasing a replacement blade, make sure you get a blade designed to spin in the appropriate direction.
You shouldn't need any specialized tools, other than possibly a pair of retaining ring pliers.
If there are screw/bolts used to retain the blade. Depending on the rotation direction of the motor, you may encounter some left handed threads. So watch out for that.
If you get the unit running again, but notice it's not cooling.  First check that the blade is moving air through the unit in the proper direction, then call an HVAC tech to check the refrigerant charge.
WARNING:
Before beginning any work, make sure you remove power to the unit, and have verified that it's off. It's also recommended to discharge the capacitor(s) in a safe way, before poking around.