This is a great question, which no doubt has great ramifications.
I believe that there is a general assumption that for any "Ḥaloth Shem", as it were (no pun intended), there needs to be a Kinyan. In plain English, that means that for Halachah to recognize a status change in anything there needs to be a formal act of acquisition. Since a name isn't conferred in this way, my gut (and my brain) tells me that, along the lines of YDK's point, while a naming ceremony is important for demonstrating the "official" point of origin for a name (perhaps useful in a case of doubt), the actual name that is used is what has the most Halachic weight. If that is true, then in a case of controversy, if two names are declared in competing "official" declarations, either by divorced parents or just arguing family members, the name that is used throughout the person's life would be the one that "counts". If they are both adopted by the person at some point, it might be of some Halachic importance to try to determine - probably with yet a third naming ceremony later on - what the proper order of the names is, or if one is to be regarded as a nickname.
EDIT: Please see the following link for an article by Rebbi UMori R' Mordechai Friedman discussing change of status via Kinyan (specifically in the case of a Jewish wedding). http://vbm-torah.org/archive/kiddushin/07kiddushin.htm. My previous assumption that there cannot be Ḥaloth Shem without Kinyan may be incorrect, according to this article, but it may shed some light and further corroborate (or possibly reject) the idea I presented, namely that baby naming is something outside the realm of standard Ḥaloth Shem.