Legal Question in Family Law in California

Yes, provided you also send it to the other side or their attorney, and provided you bear in mind that it will most likely be disregarded, since requests and submissions to the court are supposed to be done in formal filings in accordance with the Code of Civil Procedure, the Family Code, and the state and local Rules of Court.

Most judges disregard and return such letters to the parties, because they constitute improper ex parte contact, which can get the judge in trouble.