There are a few problems in your code:

First of all, [30-33] does NOT match 30, 31, 32; it matches any of the single characters 3, 0 - 3, 3, which is the same as [0-3].  (The expression [...] is a character class, meaning that it matches only a single character).

Secondly, when you do /50[0-2]|5[30-33]/, you are trying to match 4 characters in a row:  5, 0, 0-2 or 5, 0-3.

I think what you want instead is:

if ($tag =~ /^(50[0-2])|(53[0-2])$/)
[download]

or more simply:

if ($tag =~ /^(50|53)[0-2]$/)
[download]

or even:

if ($tag =~ /^5(0|3)[0-2]$/)    # Note the parentheses ( ) are optiona
+l
[download]