i called B&M

They said reversing the polarity wont harm the electric motor.

They said the the probelm is that the blade is designed at an angle to maximize air flow....so if I operate it as a puller fan it will move lets say, 700 cfm, If I reverse it it will probably move 400 cfm.

So Ill just reverse polarity and be done with it. Since its mounted in the front of the vehicle it will get fresh forced air all the time, so If the cfm its down some its OK.