I don't want to confuse you, but since you are modifying the filenames, I would suggest an additional enhancement:

• Make the month number two digits eg, (2010-07) instead of (2010-7)

The reason for this is so that the directory listing sort order (alpha-numeric) will be the same as a more advanced sort order based upon the specific numeric Year and Month values.
Right now, your directory listing will come in this order:

2010-12-another-file.html
2010-7-this-is-an.html
[download]

I think you will like this better:

2010-07-this-is-an.html
2010-12-another-file.html
[download]

Of course with Perl, there are always a number of ways to do this.
Here are 2 ways that work well:

$month =~ s/^(\d)$/0$1/; # adds leading zero if there is just a single
                         # digit- otherwise has no effect
                         # *** I recommend this idea for 
                         #     your application. ****

$month = sprintf("%02d", $month); # re-assigns a new string value 
                                  # to $month no matter what
[download]

Other ideas occured to me, but I believe that these are the two best alternatives.