What is the difference between 本来 and 原来?
In my opinion, 1,2,3 can be both. 4 should be filled with 原来.
原来 could be used when you don't know something and then you find it out all of sudden. For example, 原来是你啊！ 原来是你干的啊！
本来 can't be used for this sense.
Most of time they are  interchangeable.
In your update sentence, 本来 is preferable, and 原来 is not that good. But if you put 原来 in the middle (丁鐺：&quot;是的，我原来要去百代試音的，但是我弄錯了日期，是明天,) that will be ok. This might be because if you put 原来 at the beginning of an sentence, that sounds you have found something all of sudden, which you didn't know. But actually you want to convey the sense originally.
I guess the key might be they are interchangeable within a sentence, but not at the beginning of a sentence!

丁鐺：&quot;是的，本來我要去百代試音的，但是我弄錯了日期，是明天。

Update
I feel this dictionary definition are accurate:
本来


原来，原先。

杨朔《京城漫记》：“这地方在北京南城角，本来是京城有名的风景区。”
2 . 原有的。
本来面目。
3 .指人本有的心性。
黄人《〈小说林〉发刊词》：“心理之辟，尤在昧厥本来。”
4 .表示理该如此。
本来就该这么办

原来

1 . 当初；未经改变的。
周而复《上海的早晨》：“阿英给奶奶提醒，立即退了回来，把脸盆放在床上原来的地方接水。”
2 . 副词。表示发现从前不知道的情况。
魏巍《东方》：“郭祥勉强睁开眼睛，原来担架停在一面悬崖下。”

I think this should help you a lot if you can understand those definitions in Chinese.