help! Whenever i try to apply the material and get the rename prefab prompt my editor crashes! What could i d o?
Hi Victor,
First of all, try to restart Unity. That often fixes issues like these.
If that did not help: Which version of Unity do you use?
2020.1.3f1 , it hangs even after restarting computer.
I could change it in the Scene and overriding, but i have tried again opening the prefab and applying material and crashed again, actually is more like a hung application, where the “hourglass” continues spinning and the program stopped responding.
When i get the " Rename Prefab file?" prompt on other times it doesnt hang. 
That’s an ancient version of Unity. Maybe you are experiencing a bug. I would suggest to update to the latest version of Unity 2020 or even 2021. No alpha or beta versions, though.
If you use a laptop, make sure the power chord is plugged in. Otherwise, it might be that your operating system is running the power saving mode.
If the issue persist, check if an antivirus program or a firewall might be blocking Unity.
Last but not least, run Unity with administration rights.