BRZ Sagging/Misaligned Bumper TSB 12-139-12
 

I spoke with the Kearny Mesa Subaru and they said that if I wanted to have the issue fixed I'd have to bring the car in and have it serviced there or by a certified technician. They also mentioned that I wouldn't be allowed to get the parts and do the work myself.

I don't want to bring my car in since it's lowered and has a lip kit (which I'm sure they'll find some way to destroy). Does anyone have any input that they could provide on this?

Then your car isn't getting fixed.

Warranty work required the dealer to do all the work.

visit the dealer and tell them how you had bad experience with other car dealers in past and would like to see how work is being done.
if dealer said you cannot allow to super duper danagerous work area, take all necessary pictures of your exterior right in front of service advisor and they'll be responsible for damage if something happens. this is just another way.