You do risk damage from an impact, so use very short bursts and try turning in both directions. Sometimes turning towards tightening will break the grip.
This is true. But the way I look at it is you either do something to resolve the issue, or resort to some other means of changing the oil, like mentioned above, such as using a tube in the dip stick hole, and a pump.
Myself, I would risk the damage and use the impact, gently as lynnmor suggests. Chances are the plug will come out without damage. IF not, well, then you will be forced to fix it properly I suppose.
Maybe wait until you are about done with the tractor in late summer, early fall? Then you will have some months to fix it properly, if need be.