Yes, it is possible to change the contract code in TON. Just implement it inside your smart contract that will be updating contract's code using FunC Standard Library (stdlib.fc) function:

() set_code(cell new_code) impure asm "SETCODE";

Simple implementation inside recv_internal:

#include "stdlib.fc";

global slice ctx_owner;

() recv_internal(int my_balance, int msg_value, cell in_msg_full, slice in_msg_body) impure {
	slice cs = in_msg_full.begin_parse();
	int f...