Does it have to be Date::Manip? I prefer DateTime, it has excellent time zone handling and everything else regarding date/time handling, also via add-ons like for example DateTime::Format::Strptime.

use warnings;
use strict;
use DateTime;
use DateTime::Format::Strptime;

my $strp = DateTime::Format::Strptime->new(on_error=>'croak',
    pattern => '%Y-%m-%d-%H:%M:%S %Z');
my $datestr  = "2016-07-30-15:30:00 GMT";
my $dt = $strp->parse_datetime($datestr);
print $dt->strftime('%Y-%m-%d-%H:%M:%S %Z'), "\n";
$dt->set_time_zone('America/Los_Angeles');
print $dt->strftime('%Y-%m-%d-%H:%M:%S %Z'), "\n";

__END__

2016-07-30-15:30:00 UTC
2016-07-30-08:30:00 PDT
[download]