creating Blend Shapes between Selection sets, That is something I didn’t know 
I entirely revised the scene and found out a few helpful things … please correct me if I’m wrong :
the whole body skinned character :
Method 1:
- first extract the face area , duplicate it , create a blend shape between these two then combine the original head with the rest of the body and merge it .
- then duplicate the extracted head as many times as necessary and make a blend shapes .
actually this caused me reordering inputs issues and didn’t work … by any means…
Method 2:
- creating selection set and deleting extra faces … changes the vertex number…
It deforms , and doesn’t have the ordering input problem ( blend shape the skincluster) but since the Number of vertexes change…It deforms incorrectly .
but I thought combination of these two and wrap deformer might work… here is what I did and it worked out
- I duplicated the original mesh ( full body) and make a blend shape between two.
( I reordered the input connections as well )
- without deleting the faces I just duplicated the face area and made a wrap deformer with it .
- now , time to create blend shapes with the duplicated one and finally it worked
no issues …
well for future projects I certainly will pick a straight line , I mean I will create blend shapes for the head first and then skinning and merging stuff… that is safe you know
thank you again… for your great support