You could always destroy the city...
I have tried it and it does work, though in my case it was between two of my own cities. Remember you have to exchange vans with a city with a higher base trade for the replacement to take effect.
Correct. Though there are ways to manipulate that. For example, if you know the city at the other end of your food route is the one with the least amount of base trade among your three routes, then just before delivery you pick one of the other cities that you are trading with and turn all its citizens into specialists. This would reduce its base trade and insures that its trade route will be the one that gets replaced. After delivery you put the specialists back to work.
That definitely happens. To protect my lucrative foreign trade routes, I make all the citizens of the sole domestic trade partner city into specialists, deliver, and then put them back.sometimes when a caravan got to my main trade city, I noticed that one of those 3 routes would get replaced by the new route even though the new route gave me less trade arrows than the one that was replaced. I guess that it might be because the new route was with a city with more base trade but, since it was mine instead of foreign, it gives me less trade arrows...
We, the Greeks, have accidentally made a food route to Egypt. The route goes from Sparta to Helipolis.
Why the food delivery replaced a highly profitable route in the first place I don't know, because I have delivered food between other cities many many times without creating a route.
Now I have to find a way to replace the food route, but no success so far. Sparta has built a new Freight carrying coal, but delivering it to Helipolis or another big city that demands coal is not replacing the food route. (Helipolis demands coal.)
How do I replace the food route?
(Civ2 standard, v2.42.)