This isn't merely LWP::UserAgent usage. This is basic Perl syntax. Don't get me wrong - that's still perfectly on-topic for this site (I did approve the node after all), but let's get you the help where you're at: introduction to perl. Perhaps perlintro might help.

What you probably want to do is capture every stage of that long 3rd line in separate variables so you can reuse them later.

my $ua = LWP::UserAgent->new();
my $response = $ua->head($url); #HTTP::Response type return
my $headers  = $response->headers(); # HTTP::Headers type return
my $content_type = $headers->content_type(); # string
[download]

Now you have everything separated out. You can do whatever you want with them, without re-fetching the headers.