Merg nodes from elements without loosing surfaces

Hello,
i have two elements, generated from the same or double surface with
swep, in opposite direction. Now i want to merge the nodes,
but the surfaces should not be deleted.
if i merg now every single nodes, after the last node-pair is merged,
i lose my surface!
if i merg the lines, it works only if i have min. one node not on the line,
and no influence, if i lines seperated lines or line are common for the swep area.
meshing with more elements is an option, than nodes are not only on the lines
only, but if there is another option, i would be happy!

wbr dichtstoff & thanks for your time and help


merg-01.fbd

pnt ! 0 0 0
pnt ! 0 1 0
pnt ! 1 1 0
pnt ! 1 0 0
line ! D001 D002 101
line ! D002 D003 101
line ! D003 D004 101
line ! D004 D001 101
GSUR A001 + BLEND + L001 + L002 + L003 + L004
seta A001 s A001
line ! D001 D002 101
line ! D002 D003 101
line ! D003 D004 101
line ! D004 D001 101
GSUR A002 + BLEND + L005 + L006 + L007 + L008
seta A002 s A002
elty A001 QU4
mesh A001
swep A001 part-01 tra 0 0  10 1
elty A002 QU4
mesh A002
swep A002 part-02 tra 0 0 -10 1
seta unite l L001 L002 L003 L004
seta unite l L005 L006 L007 L008
comp unite d
#merg n unite

#seta new-01 n 1  9
#seta new-02 n 2 10
#seta new-03 n 3 11
#seta new-04 n 4 12
#merg n new-01
#merg n new-02
#merg n new-03
#merg n new-04

seta nodes n all
enq  nodes check rec _ _ 0 1
comp check d
plot fa check
plus na check
prnt se

merg-02.fbd

pnt ! 0 0 0
pnt ! 0 1 0
pnt ! 1 1 0
pnt ! 1 0 0
line ! D001 D002 102
line ! D002 D003 102
line ! D003 D004 102
line ! D004 D001 102
GSUR A001 + BLEND + L001 + L002 + L003 + L004
seta A001 s A001
line ! D001 D002 102
line ! D002 D003 102
line ! D003 D004 102
line ! D004 D001 102
GSUR A002 + BLEND + L005 + L006 + L007 + L008
seta A002 s A002
elty A001 QU4
mesh A001
swep A001 part-01 tra 0 0  10 1
elty A002 QU4
mesh A002
swep A002 part-02 tra 0 0 -10 1
seta unite l L001 L002 L003 L004
seta unite l L005 L006 L007 L008
comp unite d
merg n unite

seta nodes n all
enq  nodes check rec _ _ 0 1
comp check d
plot fa check
plus na check
prnt se

hi, connect coincident nodes by using equation constraint can be an option probably.