Hi,
I could do it myself. Here goes the code

tie @array , 'Tie::File' ,  "$file" ;  

    foreach my $key (keys %varHash)
    {
        my $keyflag = 0 ;
        my $changedVal = $varHash{$key}{newVal};
        my $startdef = '<default>';
        my $enddef = '</default>';
        my $storedindex;
        
        print "key $key | changedVal $changedVal \n";
        for(my $i = 0 ; $i <= $#array ; $i++)
        {
            if($array[$i] =~ /$key/)
            {
                print "here $key \n";
                $keyflag = 1 ;
                next;
            }
            elsif ($array[$i] =~ /\<default\>.*?\<\/default\>/gs)

            {
                #    print "array[i] $array[$i] \n";
                if($keyflag)
                {
                    $array[$i] = "$startdef"."$changedVal"."$enddef";
                    $keyflag = 0;
                    last;
                }
            }
            elsif($array[$i] =~ /^\s*\<default>.*[^\>]$/)
            {
                $storedindex = $i ;
            }
            elsif($storedindex > 0 )
            {
                if ($array[$i] =~ /\<\/default\>/)
                {
                    my $range = $i - $storedindex;
                    splice(@array, $storedindex,$range);
                    $array[$storedindex] = "$startdef"."$changedVal"."
+$enddef";
                    last;
                }
            }                
            
        }            
    }

    untie(@array);

}
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