How to decrease the fish trap food amount from 715 to 72?

The modify resource fish trap food amount is not all working, even I set it or add it or mutliply it! It wont have any effect. Could you please help me out?

It still works, but as with farms, the modified food amounts are not applied retroactively. If you modify the food amount, then place a new fish trap it should work.

I just tested it, and it ~works, but there is something weird going on, depending on how you set it up. If you set it to X amount, it will end up as X+15 (e.g. 5 food turns to 20 food, 72 to 87), although if you subtract the desired amount, it does work properly (e.g. subtracting 710 from the 715 base properly gives 5 food as the result).

Aaah, it worked with new fish trap. So it is very difficult to change in the middle of the game, like hope say I have applied 6x tech and for every tech I increased an amount of 70, the old fish traps wont be effective, I need to place new fish traps. And even its just modify resource, why not modify attribute is available?