So, sending articles via messages, one by one, and when you write them all, you’ll send them all via the delivery button? That wouldn’t break the rules (just be sure to send them all via the delivery button in the end, even though you’ve already sent most of them).
They can request a cancellation through the Resolution Center (you don’t have to accept it, of course). They can also try to convince Customer Support to cancel for them. Or they can request a cancellation (through the Resolution Center or by asking CS) before you hit the delivery button, and after you’ve sent some (or all except for the last) article.