Originally Posted by Porcepic

If your ticket is a round-trip, if you do not fly the outbound leg KL rebooked you on, the whole trip will be cancelled.

Remember your rights (https://europa.eu/youreurope/citizen...ncellation-1):


You could choose between two options with KL:

• Option #1: ask for reimbursement of your original ticket. Then buy your new ticket by yourself. KL will still have to provide compensation.
  You will end with: reimbursement of the original ticket + 600€ cash compensation or 800€ voucher - cost of the new ticket
  
  Be careful, if your ticket is a return ticket, your whole trip will be canceled/reimbursed. Do not buy a single trip IAH->AGP and expect to fly back to IAH with your original ticket, it will not be possible.
• Option #2: insist on being rerouted. The EU regulation states that KL must reroute you "at the earliest opportunity". Airlines often try to believe it means "at the earliest opportunity on one of their flights" but that is not what is written. If you could find a open seat on an earlier flight, the airline must reroute you via this flight. Dura lex sed lex.
  You will end with: 600€ cash compensation or 800€ voucher - cost of the new ticket you will not use

As you have already accepted a rerouting on AA you don't want to use, I would suggest you do not request any refund online (except if the website is clear enough) but call an agent instead to be sure the cancellation is made through EU261.

In any case, KL is due to pay you the compensation. If you just don't take the flight tomorrow, KL will not reimburse the flight though and the upcoming legs of your original ticket will be cancelled. If you cancel the ticket (= whole ticket, not just the outbound flights), you may be refunded (but it may be too late as you have already been rerouted) and receive the compensation.