I see many say this but without reference.
"Know the rules well, so you can break them effectively." --Dalai Lama
Verizon Begins Charging Full Price of Warranty Phones if Rooted? (Updated) – Droid Life (TL;DR: VZW doesn't check for root)
Personally, I would revert to out-of-the-box configuration (assuming there was no hardware failure preventing such) to erase all my personal information and to avert any potential problems with troubleshooting (mine and theirs) or arguments over "modifying the device".
If your phone doesn't look like garbage and you play the minimal naive user-in-distress and be nice and respectful, I'd be surprised if you ran into support problems. Basically--speaking as a former inspector--don't give them a reason to look beyond the surface.
Edit: The Magnuson-Moss Act applies but that doesn't keep the merchant from making it difficult for you. (Mopar/Chrysler dealers are bad for blaming failures on unrelated modifications.)