chadgadya
“I don’t think there is such thing as a minhag not to do something mentioned in the gemara and shulchan aruch without any machlokes”
I’m not sure what you mean there are countless examples.
The first one that pops into my head : The Gemara says the Haftorah for Simchas Torah is Shlomo’s birchas Hamelech there is no machlokes in the Gemara. I am certain that isnt what your shul lains.
“there is no doubt that nowadays everyone should eat all the simanim that are obtainable.”
There is doubt. First and foremost because we arent sure what they all are.
“The carrots were a substitute for the unavailable rubiya, because it had the SAME meaning in yiddish”
ok, but this isnt brought in the Gemara nor shulchan aruch