It’s important to know that there are national warranty laws that say that a manufacturer cannot require you to use their brand of fluid to maintain your warranty. That said, there are two things that may affect your warranty.
Using the wrong type of fluid may void the warranty. Going back to radiator coolant, the correct type protects against corrosion and the wrong type will not. So it’s important to be right.
Also some warranty protections are conditioned on taking care of scheduled preventive maintenance. Please review your warranty if you have questions.