move and rename files with current date appended to file name

The way I interprete your problem is: you want to make backups of a certain directory and you want add a datestamp into the filename.  Untill now, you used the current datestamp [the moment when you copy your file], but now you want to use the datestamp that is indicating when the file was modified for the last time.  Correct?

### option 1 ###
If you just want to remember the datestamp [i.e. *not* explicitily mention it in your filename] and you want to *move* and *not* copy the files, you can use "rename $file "C:\\......" because when you use rename, the datestamp of the original file is maintained [in contrast with copy, where the datestamp of the new file will correspond to the current time].
 
### option 2 ###
you want to copy the files to your backupdirectory AND you want to save the datestamp of the original file.  In that case you can use the "stat" -function in perl.  This stat-function gives you a lot of information concerning the file of interest.  You have to add "use File::stat".  This is what i added to your script:

my $info = stat($file);
my $datestamp = strftime(".%Y%m%d.%H%M%S", localtime($info->mtime));

you can print the datestamp of your file via:
print "date file last modified --> ", localtime($info->mtime), "\n";  
this will give you something like: Thu  Jan  8  09:21:28  2004

when you do
my $datestamp = strftime(".%Y%m%d.%H%M%S", localtime($info->mtime));
this will give you: 20040108.092128 [equivalent to the date mentioned above Thu  Jan  8  09:21:28  2004]

This time is the time when the file was last *MODIFIED* because you use "$info->mtime".  When you want to have the date the file was last accessed, you have to use "$info->atime".


--- this would be your script ---

#!/usr/bin/perl -w

use strict ;
use POSIX ;
use File::Copy ;
use File::Basename ;
use File::stat

chdir "C:\\work\\bus_cov_data_in\\bus2111\\trans_cidX"
   or die "Can't chdir to C:\\work\\bus_cov_data_in\\bus2111\\trans_cidX $!\n" ;

for my $file (<*.xml>)
  { my ($name,$path,$suffix) = fileparse($file,"\.xml") ;
   my $info = stat($file);
    my $datestamp = strftime(".%Y%m%d.%H%M%S", localtime($info->mtime));
    copy $file,"C:\\work\\bkups\\bkup_bus_cov_data_in\\bus2111\\trans_cidX\\$name$datestamp$suffix"
      or warn "Cannot copy $file $!\n" ;
  }

--- end of script ---

Good luck!