You could do it in a simple subtitution:

$file =<<EOF;
<ins cnt="4">
blah
<ins cnt="2">
EOF
                                                                      
+          
$file =~ s/<ins cnt="(\d+)">/"<TAG>" x $1/egs;
                                                                      
+          
print $file;
[download]

Note the /e modifier to the substitution that permits the evaluation of code in the RHS.

/J\