After surfing through internet around generic approaches for customizable characters I found out that there is no an “out of box” solution. It’s up to character designe to how you would like to change its appearence. If you want to use a singl-mesh character and simply add for example a jacket mesh → you have to take care about every single frame in every possible animation to be sure that character’s skin doesn’t shows up through jacket on shoulders and elbows. If you want to use multi-part character and replace “naked chest mesh” by “jacket chest mesh” → you should take care about how to deal with vertex seams :-/ I choosea multi-part approche cause I can’t struggle anymore with animations.
Finally I ended up with a bit different approach from my previous comment: I took a regular high-poly normal map, but in order to leave all vertex normals on the seam untouched I cutted mu dude’s neck one loop below the seam loop and scaled that cut loop a bit down so this extra loop was hidden by the chest mesh. To create the chest mesh I cutted the neck on the loop above the seam loop, and again scaled cut loop a bit down. As the final result, dude’s head mesh is penetrating a bit inside the chest below the seam, and the chest is penetrating inside the head mesh above the seam, which is actually bringing a quite acceptable result regarding the lighting 
I’ll post some description pics a bit later.
Personally I found this work around quite usefull cause it not depends on 3D application you’re using → they all use vertex normals the same way. Well… latest version of Blender DOES has normals manipulation tool, but it’s still too rough and lack of control.