Given MAC-48 format, using either colons or hyphens, how about a substitution:

$ perl -le '$re = qr{(\S\S)[-:](\S\S)[-:](\S\S)[-:](\S\S)[-:](\S\S)[-:
+](\S\S)};
    $str1 = "28:8a:1c:59:cc:85"; $str2 = "28-8a-1c-59-cc-85";
    ( $cat1 = $str1 )
      =~ s/$re/$1$2.$3$4.$5$6/;
    ( $cat2 = $str2 )
      =~ s/$re/$1$2.$3$4.$5$6/;
    print "$str1 is now $cat1\n";
    print "$str2 is now $cat2\n";
'
__output__
28:8a:1c:59:cc:85 is now 288a.1c59.cc85

28-8a-1c-59-cc-85 is now 288a.1c59.cc85
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Too ugly??