If the CEO sent an email about new "Capricious and Arbitrary Referral Bonus" then I'd tend to agree with you that the OP should have expected to be treated in a capricious and arbitrary manner in regard to the payment of the bonus.
For example in my options contract with my last employer it stated that the options were part of an employee retention program and should not be construed as remuneration.
After reading those lines I knew the options were a ploy to retain employees and not to actually expect to make a cent from the options. Upon quitting and being offered to buy out my options I said "The options contract states that it's for retention and not remuneration, why would I buy something that you've warranted as worthless?"
It's no different than an employer offering a 'bonus' for hitting a certain date for code. If I quit day after delivery it should make no difference as to whether I'm paid.
Bonuses are when you receive additional pay for performing your required duties as an employee. eg. you were hired as a programmer, you've doing great work, here's an extra 10K.
Not only did they fail to pay your wages within X days of termination, an egregious violation of the labour code but now they are misrepresenting the employment agreement as not including written amendments made by officers of the company.
Furthermore this policy they speak of has altered the employment agreement with out consent from the employed, and failure to disclose the policy at the time the offer was made constitutes negligent misrepresentation of the contract. I'm sure if you had known that you would have only received payment while still an employee, the offer would not have induced you to perform said services for the company. Failure to inform employees of changes to the employment agreement is also likely a violation of labour law.
File with your local labour board for unpaid wages, dealing with this should cost them easily more than $10K. The last thing they want is bureaucrats around their business.
Then file in small claims court for lost wages and breach of contract.
Attach the directors of the corporation personally to the suit as directors are liable for unpaid wages. (This may not be true in your jurisdiction)
Find the statute that says that all unpaid wages must be paid within X days of quitting / termination, add damages.
Add up all your time spend dealing with the recovery of this money, as well as reporting this to the authorities, add costs.
Hopefully after this you've reached the max allowable for a small claims suit.
I am not a lawyer, this isn't legal advice.