TriggerToChangeRecordType

trigger OppTrigger on Opportunity (after insert, before update) {

  Map<String, Id> typeMap = New Map<ID,RecordType>();
  for(RecordType rt: [Select ID, DeveloperName From RecordType Where sObjectType = 'Opportunity']) {
    typeMap.put(rt.DeveloperName, rt.id);
  }

  for (Opportunity opp : trigger.new)  {        
      // And the Agreement Category on the record = TEST
      if (opp.Stage__c == 'Negotiation/Review') {
        // Then automatically change the Record Type to ReadOnly RecordType
        opp.RecordTypeID = typeMap.get('ReadOnly'); 
      }         
  }
}