Iconography, to get back to the subject at hand, is a specialist style of painting and people do study it, and they do get apprenticed. A friend of mine is a modern day iconographer, and does work for churches both original icons and frescoes as well as restoring older ones. Doing frescoes is gruelling work, often they paint lying down, looking up at the ceiling for days on end.
Part of the learning is involved in discoverin the materials and techniques used by the iconographers of the past so that the same materials can be used to day, especially in restoration work.
As for the looting of churches, several people in the north have turned it into a major export business. It is not just a case of vandalising the enemy's monuments. Icons from churches have turned up in the antique stores in almost every major city in Europe and the USA and some even in Athens via Istanbul. Which leads one to ask why not employ a modern day famous iconographer to make a copy, sign it and thus have the icon and also leave the original alone.