Yes you can change the prop through the weed hatch, I have done it twice.
It will necessary to have the drive shaft connected to the engine.
Remove the split pin - remove the nut and washer - turn the prop until you have the key & keyway at the top - mark this position on the drive shaft inside the engine bay. Replace the nut a couple of turns - now you need a wedge to drive between the hull bearing and the prop. I have used a mooring pin - the prop is on a taper and the shock of an hammer blow should loosen it. As soon as you break the taper the prop will be loose. tie a rope around the prop and secure it to something in the boat. Remove the nut and making sure the keyway is at the top and slide of the prop, remove the key.
After the replacement of the new prop, the major problem in changing the prop through the weed hatch is finding the hole for the split pin, if it in a castle nut it is easy - if it is drilled through the nut you may have problems. You may have to buy or make a castle nut.
Good luck
Alex