Don’t do that. It’s not sensible, ulimately, and there are ways to do what you want.

You probably want default_header(s) in LWP::UserAgent (and WWW::Mechanize is a nicer subclass of it). If you want better HTTP::Request shortcuts, try HTTP::Request::Common

use strictures;
use LWP::UserAgent;

# my ($content,$decoded,$req,$res);
# ^^^ No! Nothing in the full scope, please.

my $ua = LWP::UserAgent->new;
$ua->default_header('Content-Type' => 'application/json');
$ua->default_header('Accept' => 'application/json, text/javascript, */
+*; q=0.01');

while ( my $url = your_url_generator_lister() )
{
    my $response = $ua->get($url);
    # do whatcha gonna do with it.
}
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