When you say the consultation process will become the manner in which senators are appointed, there are two possible meanings. One meaning is that you go to the power of the Governor General, which is mentioned in section 24, in which case it's clearly over the line. The other interpretation is to say that you're trying to bind the Prime Minister to giving the advice that flows from the consultation process, and that, I would say, is a grey area.
On the one hand, you could argue that the powers of the Governor General are not touched, that section 24 only concerns the powers of the Governor General and that they don't include anything that happens before the legal decisions that the Governor General will make.
On the other hand, you could argue that the power of the Governor General under section 24 includes the right to be advised by the Prime Minister and the right to be given advice that's free.