$ perl -le'
$_ = q[ <csp c="3"> ];
print;
s{<csp c="(\d+)">}{ join "", map qq[<colspec colnum="$_" colname="col$_"/>], 1 .. $1 }eg;
print;
'
 <csp c="3"> 
 <colspec colnum="1" colname="col1"/><colspec colnum="2" colname="col2"/><colspec colnum="3" colname="col3"/>