I'm gathering that there isn't a 100% consensus on some of these things. Which is fine, I don't have a problem in tinkering with the system. So, just to sum up my thoughts (and a bit of tinkering).
You can declare aspects on an NPC, with using a skill roll and a standard action - just like a maneuver. This gets a free tag, and if sticky - may last a long time, depending on what the player wants and what the DM agrees to.
You may also do it as a free action, by using a Fate Point. This requires no skill roll, and may or may not last a long time, as per the previous.
This applies in hand to hand combat if you have the Martial Arts stunt. You could possibly do this in other situations, too. ("DM, can I use my Guns knowledge to put the aspect "Misaligned Barrel" on his .45? That model is known for that flaw, maybe?")