It is difficult to answer your questions, but I will try.
What was named the Doom of Mandos was in parts at least only a telling of the future. Mandos did reveal to the Noldor, that one day they had to leave Middle-Earth because the realm of Men would begin. And he told them what would be result of not leaving Middle-Earth. The process is named fading and could be described as the slow but constant loss of physical substance. The result in the end is the naked fea of the elves which not to be seen by men save the elf desired it and the men had a special talent for it.
In so fare the doom of Mandos applied to all Elves in Middle-Earth.
Further Mandos told the Noldor that their war on Morgoth was hopeless and he showed some things that would befall all that followed them in this war, like treachery and mistrust of one against the other. To this applied the reference of Doriath falling under the Doom when Thingol desired the Silmaril.
The addition that the Noldor would learn what death by violence is and that their dead would be held long in waiting by Mandos because of the rebellion of the Noldor, was only a reminder of the law or showing that this law would applied to the Noldor under than band. That it also applied to any other elves how had done some misdeeds like Saeros does not mean that he was considered a reble-Noldor.
I hope that was a bit helpful.
Respectfully
Findegil
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