package MyBaseClass;

sub open_for_reading_validation_spec {
    return { 
        'path' => 0,
    };
}

sub open_for_reading {
    my ($this, $params_ref) = @_;

    $params_ref ||= {};
    Params::Validate::validate($params_ref, $this->open_for_reading_validation_spec);
    return $this->do_open_for_reading($params_ref);
}

sub do_open_for_reading {
    my ($this, $params_ref) = @_;

    return $this->get_context('path' => $params_ref->{'path'} || $this->path);
}


package MyDerivedClass;
use base qw(MyBaseClass);

sub do_open_for_reading {
    my ($this, $params_ref) = @_;

    my $context = $this->SUPER::do_open_for_reading($params_ref);
    if ($params_ref->{'join_longcalls'}){
        ... modify context
    }
    return $context;
}

sub open_for_reading_validation_spec {
    my ($this) = @_;

    return {
        %{$this->SUPER::open_for_reading_validation_spec},
        'join_longcalls' => 0,
    };
}