Chiquita Banana and Coca-cola were one of the top hundred businesses of 1980 along with Pepsi. Don't forget that Pinochet and Reagan are still in power during this decade. Needless to say, they'll be getting all the help they need to make the United Fruit Company great again.
I misread your OP and imagined the Soviets supporting Pepsi to remove Rios Montt. I don't know what difference some Pepsi filibusters will make in the Guatemalan Civil War if not to remove Rios Montt in favour of a more moderate figure who might not be so inclined to kill tens of thousands of people.