einzelwesen’s story is not true.
The sacraments of baptism, confirmation, and Holy Orders all “imprint a character”, or leave an indelible mark on the soul. Once validly conferred, they may not be erased. (See Cans. 849, 879, 1008).
Marriage cannot be erased either. As UDS correctly points out, the annulment of marriage is a judicial finding that there was never a valid sacrament in the first place.
All sacaments, once conferred, enjoy the presumption of validity. When a marriage is challenged, there is an actual trial, before a tribunal. A lawyer is appointed as Defender of the Bond. It is his job to advocate that the marriage was valid. Against him are the party, or parties, seeking the annulment. If they can present compelling evidence - say, for example, that the consent was coerced (“Her father was in the back of the church with a shotgun pointed at me the whole time!”) then the tribunal can find that, appearances to the contrary, there was never a valid sacrament of matrimony in the first place, and issue a decree to that effect.
Needless to say, it is not enough to merely annouce that you don’t think the marriage was valid; even if both parties to the marriage wish it annuled, the trial process must still be followed and the Defender of the Bond must still advocate in favor of the marriage’s validity.
Of the seven sacraments, Baptism, Confirmation, and Holy Orders all leave an indelible mark upon the soul, and may only be conferred once. Once conferred, they may not be “erased”.
It’s possible to imagine a decree of nullity with regards to Holy Orders – if the person conferring the sacrament was not a bishop, for example, the ordination he performs is invalid.
Baptism, on the other hand, is validly conferred by anyone with the requisite intention to baptize. It’s difficult to imagine a scenario in which a decree of nullity might be sustained for baptism.
Even if it were, however, the process would begin as all canon judicial processes do: at the diocesan level, with the diocesan bisjop, his judicial vicar, and appointed judges. An appeal from that goes automatically, in the cases of decrees of nullity, to either the local episcopal conference or to the Roman Rota. An appeal from the Roman Rota goes to the Supreme Pontiff.
(Note: if einzelwesen happens to be a heads of state, a Cardinals, or a Legates of the Apostolic See, his case would be judged in the first instance by the Pope; if he is a bishop, an Abbot primate or the Abbot superior of a monastic congregation, or the supreme Moderator of a religious institute of pontifical right, his case would be judged in the first instance by the Roman Rota; see Can 1405 § 1 et seq).
In short: einzelwesen’s story is both theologically wrong and procedurally wrong. No one may “write to the Vatican”, and, without any trial or other process, obtain a decree of nullity as regards any sacrament. And with regards to the indelible sacraments, such a decree is well-nigh impossible.