Some schools may let you see your reference - many do, actually, but they don't have to. You have a legal right to request it from UCAS after your application is sent, but before that, nothing. But referees shouldn't be letting you tell them to change it - they can ask you if you want certain things including, and if they don't ask then you can suggest it. But it's up to them what they include and whether they listen to your suggestions.