my $hashref = {
    num1 => 1,
    num2 => 2

};

print "before pass1: $hashref->{num1}\n"; #prints 1

pass1({ params => $hashref });

print "after pass1: $hashref->{num1}\n"; #prints 2 but would like it to stay as 1

sub pass1 {
    my $self = shift;
    my $params = $self->{params};

    foreach my $key (keys %{ $params }) {
        $params->{$key}++;
    }
    print "Inside pass1...\n";
    print "$params->{num1}\n"; # prints 2 correct
    print "$params->{num2}\n"; # prints 3 correct
}