Getting back to the original question. Be aware of what your rights are within that 10 day period. You have the right to cancel. You do not have any stated right to change the contract's number of points. That right to cancel can legally only be exercised in writing. Your contract for sale, most likely at the end above your signtures, should provide a statement of your cancellation right, the address you need to send notice of cancellation to, and that you can also fax the notice to a given a facsimile number.
If you fail to properly cancel and the 10 day period passes, then you are bound to contiune to complete the sale made. They will likely let you back out after that 10 day period but the contract provides that, if they do, you lose everything you have already paid as a down payment.
In other words, you might be considering calling your guide and say you want to make it a 50 point contract and he might even agree. That is fine. But if you fail to send that written notice of cancellation, Disney can later require you to go through with the original contract regardless of what the sales rep might tell you. In fact, your contract also provides that the sales rep has no power to waive the written notice of cancellation required to cancel the contract.
In other words, regardless of what you do with the sales rep to do a change, it is imperative that you send that written notice of cancellation on time and also fax a copy when you mail it.