Blue Cross Blue Shield of Massachusetts, the state’s largest health insurer, has agreed to reduce a dramatic rate hike for individuals and small businesses, becoming the fourth major insurance company to reach a deal with the state after regulators rejected their initial price increases four months ago. With this latest settlement, the state has struck deals with insurers covering 90% of the small business market, which affects more than 800,000 people in Massachusetts. The agreement, unveiled yesterday, also marks a key win for Gov. Deval Patrick, whose administration fought a high-profile battle to block major health insurers from imposing double-digit rate increases on small businesses this year. But Patrick administration officials acknowledge that they need to do more to keep rates from going up in the future.