Question

Opportunity for...
OR
Opportunity of...

Answer 1

It depends on the context.

"This is a wonderful opportunity FOR Mary."
"For Mary, this is the opportunity OF a lifetime."

Answer 2

the forcast reduces the opportunity for/of earnings management

Answer 3

If you use opportunity, I would use "for" with it.

Would it be better phrased: "The forecast reduces the change of earnings management."