Is it possible to change the "instruction segment" of a c program during its execution?

According to this article, a c program has these sections:

1. Text segment (i.e. instructions)
2. Initialized data segment
3. Uninitialized data segment (bss)
4. Heap
5. Stack

The "Text segment" (or "instruction segment") stores the executable instructions of the program.

Is it possible to write a c program that access this memory region and that makes changes on it, changing the instructions that the program will execute?