Munster was handed a one-game ban if he took an early guilty plea after committing dangerous contact on Manly prop Taniela Paseka in the first half of Saturday's 42-20 victory over the Sea Eagles in Perth.
But later, the MRC received a further report that "materially alters the nature and extent of the injury suffered by" Paseka.
"Following due consideration of this report, the match review committee has reviewed the charge against Cameron Munster and, in accordance with the judiciary code, has forwarded the player an amended notice of charge for the offence of dangerous contact (grade one)," the NRL said in a statement.
The 31-year-old will now pay a $750 fine if he accepts an early guilty plea, and will avoid missing more games after returning earlier than expected from knee surgery in Perth.
The suspension initially dealt a blow to the Storm's slim top-eight hopes as they are already missing halfback Jahrome Hughes (hamstring), wingers Will Warbrick (achilles) and Xavier Coates (achilles).
Melbourne have a bye next round, but will face ladder-leaders Penrith, lowly-ranked premiers Brisbane, and top-four contenders Cronulla in their final three games.Â
Barring a mathematical miracle, the Storm will miss the finals for the first time since 2010.
Meanwhile, centre Brian Kelly avoided even a fine after he was sent to the sin bin for a costly professional foul in the opening minutes of Parramatta's 28-24 loss to South Sydney.
