> One way is by using the :eval construct in mode-line-format.

Well, its value is for a git buffer

("%e" mode-line-front-space mode-line-mule-info mode-line-client mode-line-modified mode-line-remote mode-line-frame-identification mode-line-buffer-identification "   " mode-line-position
 (vc-mode vc-mode)
 "  " mode-line-misc-info "  " mode-line-modes mode-line-end-spaces)

So I want a specific for vc-mode (while using git) modification
so I thought I need to modify 
vc-git-mode-line-string 

And there is where I failed. 
I googled around and did not find anything, this 
is why I suggested to have a customize
menu for the change....
In this list

> I don't think "git blame" can do that.

Ok I try to find out
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