As far as I know, Torquoise Hill Resources (formerly Ivanhoe), the partner of that agreement, has not agreed to any such renegotiation.
But, just for the fun of the exercise, let’s imagine how such a negotiation might play out:
Mongolian Government: “We want you to increase our share to 50%.”
Torquoise: “How much do you intend to pay for that?”
Mongolian Government: “Nothing.”
Torquoise: “Why should we be interested in giving you shares without any payment?”
Mongolian Government: “We don’t care. Just give us the shares.”
Torquoise: “It has been nice talking to you. We prefer keeping the current agreement.”
See? That would be really easy. And the result would be rather predictable.