Will having my cord upgraded void my car's warranty?
It will absolutely not void the warranty on your car. In the US we have the Magnuson-Moss Warranty Act which is a United States federal law, (15 U.S.C. § 2301 et seq.). Enacted in 1975, it is the federal statute that governs warranties on consumer products. Among other things, It prevents manufacturers from denying warranty coverage from aftermarket upgrades or parts. The only way they can deny a claim is to unequivocally prove that the EVSE did damage to your car, which would be impossible because it's simply not possible for any EVSE to modify the way the car charges it's battery. All cars that use the SAE J1772 standard have on-board charging modules (OBC) that do the actual power conversion and regulate the charging process. All the EVSE does is deliver the AC power safely to the car's on-board charger.
Secondly, if using a "non-approved" EVSE were to somehow void your warranty, then everyone who's ever charged at a public charge station would no longer have a warranty!
The whole point of the SAE J1772 charging standard is to ensure safe charging and compatibility across all brands and devices. The proof is in the fact that we have thousands of units out there being used every day, and not one single report of either a warranty problem or any damage to a car.