$file =~ s/(\w{2})(\d+)/$1 . lc($1) . $2 . lc("yy")/e;

##</code><code>##

$file =~ s/(\w{2})\d+/$1 . lc($1) . "yy"/e;

##</code><code>##

  $file =~ s/(\w{2})\d+/\L$1yy/;