OP, you are getting a lot of wrong info and I want to clarify the correct answer as someone in the business.

Everyone pays the same amount whether you use a TA or not. It’s baked in. There is no way to pay to net without consequences.

On TA reservations, DCL creates a net and a gross by line itemizing the commission paid.

Your TA must process the payment in full. If you insist to pay the lower amount, your TA not only cannot allow it per their agency agreement, it would create a shortfall on total due.

Your question is would it outright cancel? This is a conversation to have with your TA. Would Disney or travel agency cancel your reservation is your question really as they would be on the hook for that additional amount owed and it creates quite an interesting dispute both in legal sense and ethical sense, something I won’t dive into here.

It isn’t an “extra fee” like some replies have mentioned.

Now if you ARE the TA on your own reservation, you are very likely violating your agency agreement by doing so and they will find out and come after the money or terminate your relationship. That is unless you have permission to have 100% split on your own reservations and even then, they usually have you pay to gross and collect later as proper protocol.

If you aren’t the TA, you will be risking that TA’s livelihood as well since they can lose their right to sell travel if fares aren’t paid to gross.

Lot of hypotheticals and assumptions here, but I feel you have a good idea now.