If life insurance policy holder changed beneficiary and sent the signed form to the insurance company and died ten days later does the insurance company by law have to honor the changes?

Yes, the moment the owner of the policy changed the beneficiary and signed the form, the intent was made. Some companies will honor the change based on the postage date, others will honor it based on the receipt in home office and still others life Fraternal companies will honor it upon receipt and approval from the board. Regardless, the owners intent was clear when he signed the form so you should not be trying to go against his wishes.