$s = '<csp c="3">';
$s =~ s/<csp c="(\d+)">/"<colspec colnum=\"1\" colname=\"col1\"\/>\n" x $1/egs;
print $s;


output:
--------
<colspec colnum="1" colname="col1"/>
<colspec colnum="1" colname="col1"/>
<colspec colnum="1" colname="col1"/>