Can you use a cortisporin (neomycin polymyxin and hydrocortisone) ear suspension to prevent an ear infection?

No. Cortisporin (neomycin polymyxin and hydrocortisone) ear suspension is one of the treatments for a current external ear infection ("swimmers ear"), but is not used for prevention. A mixture of equal parts white vinegar and rubbing alcohol is an old tried-and-true preventative treatment.