Code:
$ cat abc.dat
a,b,C-D-E,f,g
h,i,J,k,l
m,n,O-P-Q-R-S,t,u
v,w,X-Y,z,a
$ perl -ane '@x=split(/,/,$_); @y=split(/-/,$x[2]);
foreach $char (@y) { print "$x[0],$x[1],$char,$x[3],$x[4]"; }' abc.dat
a,b,C,f,g
a,b,D,f,g
a,b,E,f,g
h,i,J,k,l
m,n,O,t,u
m,n,P,t,u
m,n,Q,t,u
m,n,R,t,u
m,n,S,t,u
v,w,X,z,a
v,w,Y,z,a
$