It is possible
Last year in February, I had my approval notice with instructions to go to Los Angeles downtown INS office for I-551 stamp. Instead, I went to Santa Ana for stamping. No questions were asked. I got it done at Santa Ana, and got the plastic card 6 weeks later without any issues.
I guess it is entirely upto the clerk who issues the tokens to let you in. I suggest not to lie to them about the city of your residency just to gain entry into Santa Ana office. They can always see your current address from your ID etc. There is no harm in trying your luck at Santa Ana. In the worst case, if they deny entry, you could always go to LA as a backup plan.
Like someone said, a few hours wait is worth, especially after several years of wait for that much awaited approval notice. My advice - go to LA office and get it done there. It is best to go there early (like 3-4 AM in the morning) so that you are not denied entry due to overcrowding. Take blankets, and a folding chair so that you can wait comfortably in the line - no public toilets nearby. The only one is across the street in a gas station. I have heard that the gas station guy shuts it down after 6 AM for public, perhaps because of all those waiting at INS crowding the toilets at the gas station in the morning.