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You are in CA and have some additional rights when it comes to interest rates and stuff changing I believe... Don't accept changes!
They can't change the terms. If they pull they we sold it crap, tell them you want your car and the deal is off or they give you what they agreed to. Do NOT sign ANYTHING!!! If not, tell them you're immediately informing Honda corporate, the DMV, and state's AG. Tell them you know exactly what they are up to. Honestly once they meet an educated customer, they'll cave. Ultimately the deal they have w/ you IS profitable and if their try to make it MORE profitable don't work, 99% they'll let you keep the deal you have.