Is it legal to modify your Avata drone and or its headset? I wanted to kinda make my drone have a ar feature where displays pop up, kinda like a tracking and lock mechanism, and i wanted to attach a robotic arm to it. I also wanted to change the antenna, so I could fly one state to another without leaving my couch.

I don't think it's illegal to modify a drone in US (it would be in EU for a drone with C label). But replacing antennas wouldn't let you fly in another state. You'd need to completely replace O4 transmission system with something based on cellular network. You'd be better off making a custom drone than modifying a DJI one as that would take a crazy amount of reverse engineering when there are open-source solutions out there.

Not sure if serious?

You are free to do whatever you need to do with you DJI drone.  It won't be illegal to "tinker" with the drone but it could be illegal the things you intend to do with a modified drone.  However, one exception I am aware of is you cannot arm or outfit your drone with offensive weapons.

Id go for it.  

Hi there. Thank you for reaching out. We do not recommend drone modification on your DJI Avata for flight safety. Please note that we cannot guarantee any stability if you perform the mentioned modification on the post. Should you have any relevant inquiries, feel free to contact us. We appreciate your understanding and support.