Fixing the one hole would be ok, as long as you pulled all the other pistons out and at least re-ringed them, and flex honed the cylinders. A customer at our shop found this out the hard way. My reason for saying this, is that the one new piston and rings would be sealing much better than all the others, therefore trying to do much more work than all the others.
My suggestion: Replace the bad piston/sleeve, and re-ring the others and flex hone the other cylinders to de-glaze the bores. While pistons and rods are out, and the pan is off, check out the oil pump and re-bearing the rod brgs. Since the heads will already be off, at least lap the valves in on all cylinders, or have them ground so that they are all sealing equally cylinder to cylinder.
My bets are that it has a cracked ring or stuck ring, and the fire is burnt behind the rings- from what you are explaining and what I have seen in the past. If you like the tractor and want it to be around a long time, don't leave the other cylinders alone or you'll be pulling it back apart in one season. It happened on a 2745 that a guy wanted to "save some money" on, and it was right back in the shop after fall plowing one season. This time it got the major overhaul that we suggested in the first place. It's not fun doing stuff twice :)
Hope this helps,