Function per parameter does not modify variables

I built a binary tree class in which I have a bfs function that runs through it. As a parameter this method gets a void (*Op) (node_BT <type> *) function pointer that will be called inside the bfs itself:

#pragma once

////////////////////////////   CLASSE NODE: ÁRVORES BINÁRIAS   ////////////////////////////
template <class type>
class node_BT {
public:
    type data;
    node_BT * right;
    node_BT * left;
    node_BT * father;
    node_BT () {
        right = NULL;
        left = NULL;
        father = NULL;
    }
};

///////////////////////////////////   CLASSE ÁRVORE   ///////////////////////////////////
template <class type>
class BinaryTree {
private:
    int nNodes = 0;

    node_BT <type> * head;

    void lrr ( void ( * Op ) ( node_BT <type> * ) , bool inverso = false ) ;
    void bfs(void (*Op)(node_BT <type> *), bool inverso = false) ;

public:

    node_BT < type > * new_node ( type data , node_BT < type > * dad);

    int insert ( type data);

    void print ( bool inverso = false ) ;

    BinaryTree ( int max_p ) { this->max_p = max_p; };
    ~BinaryTree() {};
};



////////////////////////    FUNÇÕES DA ÁRVORE    ////////////////////////

//////// Função: Gerar novo Node ////////

template < class type >
node_BT < type > * BinaryTree < type > :: new_node ( type data , node_BT <type> * dad) {
    node_BT < type > * nNew = new node_BT < type > ();
    nNew->data = data;
    nNew->father = dad;
    nNew->left = NULL;
    nNew->right = NULL;

    return nNew;
};

//////// Função: Inserir o node gerado na posição adequada ////////

template < class type >
int BinaryTree < type > :: insert ( type data ) {
    if ( nNodes == 0 ) {
        head = new_node( data , NULL );
        nNodes++;
        return 1;
    }
    node_BT < type > * temp = this->head;

    while (true) {
        if (temp->data <= data) {
            if (temp->right == NULL) {
                temp->right = new_node ( data , temp ) ;
                nNodes++;
                return 1;
            }
            else {
                temp = temp->right;
            }
        }
        else {
            if (temp->left == NULL) {
                temp->left = new_node ( data , temp );
                nNodes++;
                return 1;
            }
            else {
                temp = temp->left;
            }
        }
    }
    return 0;
};

//////////// FUNÇÕES: Varrer a Árvore ////////////
//////// Função: Percorrer (com filas) em largura root->left->right ////////
template <class type>
void BinaryTree <type> ::bfs(void (*Op) (node_BT <type> *), bool inverso = false) {

    int f1 = -1, f2 = -1; // posição atual  e  posição final da fila
    node_BT <type> *item = new node_BT <type> [ BinaryTree <type> :: nNodes +1]; // itens da fila

    node_BT <type> *temp = this->head;
    item[++f2] = *temp;

    do{
        if (temp->left != NULL) item[++f2] = *temp->left;
        if (temp->right != NULL) item[++f2] = *temp->right;
        if (f1 != f2) Op(&item[++f1]);
        temp = &item[f1+1];
    } while (f1 != f2);


}


//////// Função: imprimir os nodes ////////
template <class type>
void BinaryTree <type> :: print ( bool inverso = false) {
    //bfs ( pp , inverso );
    bfs(p, inverso);
    cout << endl;
    bfs(pp, inverso);
}
template <class type>
void pp ( node_BT <type> *a ) {
    cout << a->data << endl;
}
template <class type>
void p(node_BT <type> *a) {
    a->data = a->data + 100;
    cout << a->data << endl;
}

int main() {

    //node_BT<double> *a = new node_BT<double>() ;
    BinaryTree<int> b(1000);

    b.insert(5);
    b.insert(-7);
    b.insert(0);
    b.insert(5);
    b.insert(15);
    b.insert(1);
    b.insert(9);
    b.insert(-3);
    b.insert(4);

    b.print();

    getchar();

}

The problem is that the void (*Op) (node_BT <type> *) function pointer of the bfs parameter does not modify the received values, such as Op(&item[++f1]); when Op is a pointer to the void p(node_BT <type> *a) function. When I put only to print, using the pp function, the values print correctly, but the other function ( p ) does not modify the received parameter. I could not understand why this happens.