PHP How to delete an element from an array after copying in a new place?

Question

I'm looping in an array, filling it with data from a file. I'm trying to change the data from one cell to another and then leave the old cell empty. So far I was using this code and it worked:

$custom_array_price['b'] = $custom_array_price['c'];

unset($custom_array_price['c']);

But for this specific case it doesn't work. It deletes the data before it gets copied.

How do I make it work?

This is the code I'm trying to use now:

$custom_array_price['c'] = $custom_array_price['d'];

unset($custom_array_price['d']);

The loop looks like this:

foreach ( $custom_array_price as $custom_key => $custom_value ) {
                    $custom_value = utf8_encode($custom_value);
                    if ( $custom_key == 'a' ){
                        if ( $custom_value == "Fecha:" ){
                            if( count($recibos) > 0 ){
                                $recibos[$cont]['html'].= "</tr>";
                                $recibos[$cont]['html'].= "</table>";
                                $cont++;
                                $times = 0;
                            }
                            $recibos[$cont]['html'] = "<table>";
                            $recibos[$cont]['html'].= "<tr>";
                        }else{

                            $recibos[$cont]['html'].= "<tr>";
                        }
                    }
                    if ( $times <= 5 ){
                        $custom_array_price['b'] = $custom_array_price['c'];
                        $custom_array_price['c'] = $custom_array_price['d'];
                        unset($custom_array_price['d']);
                    }
                    if ( $custom_value == "Neto a Pagar:"){
                        $custom_array_price['l'] = $custom_array_price['k'];
                        unset($custom_array_price['k']);
                    }
                    if ( $custom_value == "A001"){
                        $custom_array_price['g'] = $custom_array_price['i'];
                        unset($custom_array_price['i']);
                    }
                    $recibos[$cont]['html'].= "<td>";
                    $recibos[$cont]['html'].= $custom_value; 
                    $recibos[$cont]['html'].= "</td>";
        }
        $recibos[$cont]['html'].= "</tr>";

Another part of the code. Where the csv file is being read and the data is being copied:

$recibos = array();
    foreach($data_rows_price as $key => $value){
        $times++;
        for($i = 0; $i < count($value); $i++){
            if(array_key_exists('mapping'.$i,$ret_array)){
                if($ret_array['mapping'.$i]!='add_custom'.$i){
                    $new_post[$ret_array['mapping'.$i]] = $value[$i];
                }
                else{
                    $new_post[$ret_array['textbox'.$i]] = $value[$i];
                    $custom_array_price[$ret_array['textbox'.$i]] = $value[$i];
                }
            }
        }
        for($inc = 0; $inc < count($value); $inc++){
            foreach($keys_price as $k => $v){
                if(array_key_exists($v,$new_post)){
                    $custom_array_price[$v] = $new_post[$v];
                }
            }

        }