Chadgadya
1. I disagree with both of your premises. We practice what our Grandfathers did.
“as far as I know it is a clear historical fact that the so called “minhag”…” Many minhagim are like that. do you opose using a spoon feather and candle to search for chametz? (yes theres a differecne between doing and not doing)
2. I am not saying you should stop eating it or that there is an issur. I am just answering your original question “Why would I leave any out ” IT could be becasue your family doesnt eat a paricular one, It could be because you dont know what it is, it could be becasue you dont like it.
Are you saying there is a chiyuv to eat each of the simanim? I suppose that would mean a kezayis of each, (ain achilah pachos mikezayis) do you have extra shiurim cards for all of the simanim?
“Making up your own simanim is cute”
Thats what the OP wanted,
You provided a few thanks
Though for Liver some chasidim eat becasue “Leib ehrlich” (yiddish for liver – live righetously)
OF course there are other simanim tat Rebbes ate. See nitei Gavriel and the book “Rosh hashana secrets”