To replace text (if you know the place) easiest way is to use 's///'. In this case (last 10 letters).

# expecting that $file has file name.
open (INF,"$file") or die "Unable to open \'$file\': $!";
open (OUTF,".temp_file") or die "Unable to create temp file: $!";
my $line=readline(INF);
chomp($line);
# if windows remember to $line=~s/\r$//o;
# now change the last 10 characters from first line
$line=~s/.{10}$/$file/;
print "$line\n";
# this reads every line in file and prints it as is
while (<INF>) {
  print OUTF "$_";
}
rename (".temp_file","$file");
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Update
Forgot to remove the '.wra' part from what is written in file. So to fix that add following between $line substitution and print.

# remove all the character after last dot
$line=~s/\.\w+$//o;
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