Hi,
From a one half of a model I did a ALT-D copy, modelled
one half and got the same changes on the other half.
After that I CTRL-j joined both. At the seam in the middle
I did many SHIFT-s Selection-to-Center and then a W
remove doubles.
So far … so nice ?
I got some vertice at the seam of the two halfes where
edges concentrate like legs of a spider at the spider’s
body.
I want to “split” those vertice in two (or more) vertice
and takeing the same count and pairs of edges (spider’s
legs) with them.
How can I do this most efficiently and without the need of
remodeling too much ?
Another question came up while makeing the seam:
Is it possible to “Selection to Center” many vertice a the
seam that way, that only movements of the vertice
in one or two directions are allowed and others not. That
way it would be possible to close a seam in one go witout
getting a wadded handky then… 
Keep bnlendering!
mcc