C :: Setting Character In Malloc Char Array

I am attempting to change a character in a character array.In the code below, there are three attempts to do this. Only the first one will succeed. The last two both segfaults. If I understand correctly, str_one is declared in the heap, and could therefore be manipulated; and in contrast, str_two is declared in the stack and is therefore immutable, thus the segfault, when update it is attempted. However, I understand that using malloc, one is able to assign a pointer and allocate space in heap memory. Thus, I should be able to manipulate the assigned variable str_three. Doing so, however, results in a segfault.

Code:

#include <stdio.h>
#include <stdlib.h>

int main (int argc, char const* argv[])
{
char str_one[4092] = "This is string number one";
char * str_two = "This is string number two";

[Code]...