If you're asking about the direct legal consequences of the "Blutschutzgesetz" (Law for the Protection of German Blood and German Honor) - it did not apply retroactively, no.
The declaration that marriages entered into being null only applied to marriages entered into despite the law, i. e. after it took effect. (And technically, the last sentence about the public procecutor meant that the spouses could not file action for annulment themselves).
For reference, here is my rough translation of § 1 of the Blutschutzgesetz:
(1) Weddings between Jews and citizens of German or similar blood are prohibited. Marriages entered into in spite [of the prohibition] are null, even if they have been entered into in a foreign country to circumvent this law. (2) Proceedings for annulment may be initiated only by the Public Prosecutor.
While the legal status of existing marriages was not changed, the laws introduced the notion that the government had an urgent interest in protecting "German blood" and that intercourse between "jews" and "Germans" was a danger to important public interests.
We shouldn't underestimate the damaging social and psychological effects of these laws.
It is important, too, not to overestimate the exact words of NS laws. The intent was well understood by the bureaucracy and the courts.
Also relevant: The other "Nuremberg law", Reichsbürgergesetz, which did affect mixed-"race" families, and the 1938 "Ehegesetz" that declared the racial status of "Jewish" spouse reason for divorce.