Aiming in Mongoose Traveller is just aiming, just the +1 (or more if you do it successively) to hit. Nothing else, you don't have to, or even get to, pick a body part.
Called shots are not a thing in Mongoose Traveller core rules anyway.
So I guess I can see why you're asking, if you're wondering if called shots don't exist because Aiming is synonymous with it, but the answer is still no. Aiming is just Aiming.
My general impression of MgT is it's written more in natural language than in the rules-legalese of, say, Pathfinder or late edition D&D. Which means that, while they can still be unclear, you'll rarely go wrong taking something that is clear at face value, and rarely get it right by wondering what they're
really trying to say. What they're really trying to say with "Aiming is a +1 to hit for each successive Minor Action" is "Aiming is a +1 to hit for each successive Minor Action - and that's all."
Also, remember that Effect adds to damage, so if you do hit above the target number after aiming you are getting a plus to damage as well already. There's no intention of a way to double up on that plus to damage.
Kilemall, what edition(s) are you using Striker with? It's crossed my mind before to dig into Striker for Mongoose and seeing if I could reconcile them, but it's always seemed like a major project and I haven't gotten to it.
Police Officers are taught to shoot for Center Mass.
At least partly because accuracy notoriously degrades from the range to live fire, even for skilled marksmen, so aiming for center mass is not so much a way of sniping the heart as it is a way of trying to just hit
something on the target. Center mass contrasts with "just shoot them in the leg"/"shoot the gun out of their hand," which is a recipe for misses and stray bullets.
All of which is to say, aiming for center mass is almost the opposite of a called shot, just a strategy for hitting anything at all.