You seem to be talking about both apples and oranges, and lemons and limes.
As far as I know FIDE never uses U.S. Chess ratings (nor ratings from any other nation’s rating system) to initialize FIDE ratings. FIDE just waits until the player has played in a FIDE-rated event or two and then assigns a rating based on their own internal calculations. Somebody in the know please correct me if I’m wrong about this.
Going the other way around, I’m pretty sure U.S. Chess occasionally uses a player’s FIDE rating to initialize his U.S. Chess rating, but only if the player would otherwise be unrated in U.S. Chess (or perhaps provisional based on fewer than N games, and I don’t know what N is).
Above all, I’m pretty sure U.S. Chess never tries to tell FIDE what a player’s initial FIDE rating should be.
Adding a player’s FIDE ID to his U.S. Chess record, in cases where the former was missing for any reason, is (or would be) simply a useful service U.S. Chess performs (or could perform) for everybody’s benefit (the player, the TD, FIDE, etc).
Bill Smythe