There's a really good book called Thrown Among Strangers that documents the Californio experience in regards to what you're talking about. It's been a while since I read the book but iirc the Mexicans of the Los Angeles area were basically overrun by American immigrants (legal and then illegal) years before the war started, and it was generally accepted as an eventuality that California would become either American or British before too long.

One cultural aspect that changed drastically with the arrival of the Americans was in land ownership. Mexican attitudes towards it were very casual and left a great deal of interpretation as to where one's property's boundaries lied. After the war, Americans took great advantage of this to deprive Californios of their land in order to commodify it. You might recall that maximizing the profitability of land was one of the reasons for the call of manifest destiny.

Ironically, the commodification of the land went so far that even the American settlers who started this trend began to resent how drastically the way of life had been changed and began to pine for the good old days when the pace of life in Southern California was much more seigniorial and easy-going. They began to have festivals in which they would dress up as the original Californios and participate in horsemanship competitions - a prized skill among the Californio caballeros.

Money was another aspect of life that changed greatly. Before the American takeover wealth was measured in cows and, due to a favorable environment, there were so many cows in the area that most landowners could consider themselves rich. In fact, they wouldn't usually mind if someone killed one of their cows for food as long as they left the hide for the owner to retrieve. This practice became so common that the hides were often referred to as Mexican dollars.

Americanization, however, changed this too. California was opened up to larger markets and the cattle industry boomed to make the Mexican ranchers quite wealthy as long as they were able to hold onto their lands from American settlers. Retaining their lands was not an easy thing to do since court hearings were held in English in distant San Francisco with racial prejudice often playing a role in verdicts. Most Mexican landowners found it easiest to marry daughters to Americans in order to keep their lands "in the family" so to speak.

I wish I could say more but it's been a while since I read the book. I'm on my phone now but I'll edit this post later to provide more information about the book.