> Can you even do your own flush on the cooling system in a Tesla without voiding your warranty?

Good question. But you don't ever have to! https://teslamotorsclub.com/tmc/threads/battery-coolant-does...

But to answer your question YES you can do your own maintenance.

"How Much To Service Your Tesla? " https://www.youtube.com/watch?v=meJp2lj_NnM

This myth about owners not being able to perform basic (pretty much non-existent) maintenance on Teslas is way overblown.