# OP
%hash = (
        ('abc' => 7) if (! $i), # abc if not $i
        'hk' => 5,
        'jk' => 6

# Anonymonk
%hash = (
    $i ? (abc => 7) : (), # create abc if $i
    hk => 5,
    jk => 6,
);

# /me thinks
%hash = (
    $i ? () : (abc => 7), # create abc if not $i
    hk => 5,
    jk => 6,
);