Legal Question in Real Estate Law in California

The person that owns the house can have you arrested for trespass and sue you for any damage that you cause.

Perhaps you could be arrested for trespass -- or possibly even burglary -- but more likely than not, either the police or the DA would ignore the case or tell the owners that "it's a civil matter" and refuse to investigate or prosecute. That would leave it to the new owners to file a civil lawsuit against you, probably for (civil) trespass, and the case would probably be filed in Small Claims Court (if at all).

Don't forget that property may be "abandoned" in the sense that no one lives there or takes care of it, but it is never abandoned in the sense that it has no owner. All real estate has an owner.

If you have concerns about the appearance or safety of a neighboring house that is uninhabited and unmaintained, I'd suggest contacting the owner(s) for permission to change the locks or take whatever safety-related steps you think would be helpful -- and send them the keys. Possible ways to determine current ownership would include checking the tax assessment rolls in your county, which in many counties can be accessed, at least in part, on line.