Explain it to who? The couple is not your "department head" it is not appropriate for a DJ to be seeking arbitration of their disputes in the middle of the event when the couple has put someone else expressly in charge.
Most of the weddings I do don't have an onsite planner, or I am the onsite planner so, I know that plans often need to change as the event unfolds. Have the decency to allow others the same professional judgment. I'm a big proponent of communicating with my customer, but if they have designated someone to be my contact point - then I am sure to respect that. The same goes for room captains (venue managers.) If something differs between their plan and my own it is the room captain who should approach the couple to resolve the mismatch - not the DJ. The rules of etiquette aren't changed simply because a given DJ is a control freak. The issue of how to communicate with the couple should already be resolved before we step on the property.
Two things:
If the change is something you don't like or want - TFB. Be a professional and make it work. Too often I read stories here about DJs who deliberately undermine planners they don't agree with. Hopefully that returns to them in the form of accurate reviews and lack of future business.
If the requested changes are something that lie outside our skill set, we are not equipped, or otherwise are unable to deliver the changes - then be honest and SAY SO. Allow the planner to work a solution within those limitations rather than misdirect and deflect the situation into an ego protecting dispute. Pretending the real issue is the change itself, when in truth we are simply not able to make that change - is just as dishonest and unprofessional as deliberately planning to fail.