Issue in Updating CI 2.2.1 to 3.1.13

My CodeIgniter application is quite outdated, so I'm trying to update it to the latest possible version. I'm encountering the following issues:

• For multidimensional forms, it now requires `[]`. The problem is that my system is quite large. Do I really have to change this throughout the entire system?
  
• Previously, callback functions accepted multidimensional fields coming from the form post, but now they are receiving null. Here's an example:
  

PHP Code:

public function index()
{
    $this->load->library('form_validation');
  
    $this->form_validation->set_rules('skills[]', 'skill', 'callback_skills_check');
  
    if ($this->form_validation->run() == FALSE)
    {
        $this->load->view('my_form');
    }
    else
    {
        $this->load->view('formsuccess');
    }
}

public function skills_check($arraySkills)
{
    if (in_array('Strength', $arraySkills)) {
        $this->form_validation->set_message('skills_check', 'The field {field} must contain the word "Strength"');
        return FALSE;
    } else {
        return TRUE;
    }
} 


Is there any way to minimize these problems so I can use the most current version?