Automobile insurers cannot change the terms of a policy during the first two years of a guaranteed two-year policy period unless both the consumer and the insurance company agree. Ohio has statutes that forbid this.
In a recent case in Cuyahoga County, the Eighth District Court of Appeals ruled that an auto insurer could not change the policy to exclude a particular driver in the household during the first two years of the policy. The excluded driver was involved in two accidents and the insurance company refused to cover those losses. However, the provision excluding the driver was not in the original policy, but was added during the two year guaranteed period. The court of appeals ruled that this exclusion was not valid and provided coverage to the "excluded" driver.
For complete details, see http://www.sconet.state.oh.us/rod/docs/pdf/8/2012/2012-ohio-1062.pdf