Legal Question in Real Estate Law in California

You need to be more specific here. What type of loan? Assuming responsibility for what? Generally speaking, if you have a written loan agreement, the terms cannot be changed unless it is in writing and signed by both parties. But your agreement might be different.

Your loan agreement is a contract The right or power of one party to a contract to modify its terms without the consent of the other is very limited, although there are legal principles under which this could happen, such as "waiver" and "estoppel," but these are unusual.

I really don't know what you're asking, nor why, but if you told the bank you were borrowing the money for one purpose, e.g., home improvements, and you decide to use the money for buying stock or taking a vacation instead, you are probably committing an act of default under the terms of the loan contract.