Per proper procedure, I seriously looked at doing that, and am actively very annoyed that I'll be "losing" miles by only needing to fly to DFW. However, my flight into IAD arrives too late to get back out that night, and there is significant benefit to me to get into DFW sooner.

What about calling United and telling them that my plans have changed, and that I will only be taking the first 2 legs, could they please cancel the 3rd, as I would like to book a new flight with United.

Need to do so, because they want more in the fare difference than the new flight costs. Then tack on a $450 change fee, and it would cost me over $1080 instead of $550ish to just buy the new ticket.

Opinions? Would United be willing to formally cancel my last leg, without any risk to the first 2 legs?