What code of honor?

In the first scene of the Trilogy, Vito seems to establish some sort of code when he admonishes Bonasera for asking for murder in retribution for an assualt which did not kill his daughter.

But, minutes later, Michael tells Kay about Vito using the threat of murder (surely not a bluff) in a financial matter (incidentally, to allow Johnny Fontaine to break his word).

The Dons like to use the code to seperate themselves from common criminals but it's pure hypocrisy, as the code is ignored whenever it would interfere with business.

But, to answer the question, I believe that Vito certainly broke the spirit of the oath he made at the Commission meeting, if not the letter of it.