You don't say how you want to match it. Anyhow, this is the basics of the replacement:

• use the -i flag, or set $^I to a defined value
• put the path of the httpd.conf file in @ARGV
• loop through <>
• edit the lines you want to change
• and print

Code:

{
    local $^I = ".bak";
    local *ARGV;
    @ARGV = "/path/to/httpd.conf";
    while(<>) {
        s/^(?=.)/# /;   # simple substitution
        print;
    }
}
[download]

You'll probably have to make the rules for the update more complex. Here's one way to match a <Directory> block. Put the following code block inside the while(<>){ ... } block:

if((my($dir) = /^<Directory\s+(.*)>/i) ... /<\/Directory>/i) {
    if(defined $dir) {  # first line in the block
       for ($dir) {
           s/^"//; s/"$//;  # remove quotes
           $icons = m(/icons$);
       }
    }
    if($icons) {
        ... # do something with these lines
    }
}
[download]

$icons may not be declared inside the loop, or it'll be undef next time you go through the loop.