If I had dogs going on long hikes in the mountains, there might be some shots/precautions I might consider. For an elderly dog that stays in the yard, the risk analysis is different, and in my view in your case the risks far outweigh the possible benefits.
I personally would skip the distemper shot, being fully conscious that failure to get the shot could potentially cause problems.
There are always trade offs, risk of "Occurrence A" happening vs. risk of "Occurrence B" happening.
Risk is not avoidable, so it's better to come to peace with the fact that sickness may result from NOT getting the shots, knowing at the same time that the risk of getting sick from the shots is even higher.
Plus, MaxaLisa is right, your dog is highly likely to still be protected for longer than the 3 years stated.