Constants are, um, constant. So if the argument of LOAD_CONST is immortal is will always be immortal.

We could add a specialization of LOAD_CONST, LOAD_CONST_IMMORTAL, which doesn't do any refcount modification.

The neatest way to do this would be in the compiler, but it can be done at runtime:

inst(LOAD_CONST, (-- value)) {
    value = GETITEM(frame->f_code->co_consts, oparg);
    if (_Py_IsImmortal(value)) {
        next_instr[-1].op.code = LOAD_CONST_IMMORTAL;
    }
    else {
        Py_INCREF_UNCONDITIONAL(value);
    }
}

A LOAD_CONST_MORTAL specialization is not possible, as PEP 683 allows mortal object to become immortal.