UPDATE 1-Guatemala to present mining law changes despite objections

* Government to present proposed mining changes to Congress * Mining industry says investment will be stifled * New projects, not existing mines, would be affected By Mike McDonald GUATEMALA CITY, July 5 (Reuters) - Guatemala's government said it will move forward with a proposal to acquire as much as a 40 percent stake in new mining projects despite a push back from mining industry representatives who say the plan could stifle future investment. President Otto Perez will p