"耶“ is used in this sentence as a modal particle without any actual meaning. Usually, if you want to show your cute, your can add "耶” in the end of your sentence. For example "你好美耶···“, that means "you are so beautiful".

sometimes it shows the person is excited and superised, strength the tone of the sentence

北方人一般不习惯在句尾加‘耶’，而且听到有人这么说会觉得somewhat awkward。 但是南方人和台湾人好像经常喜欢在句尾加‘耶’，但都是特别轻松愉快的场合以及和熟人之间。 Anyway，耶放在句尾听起来有点嗲（speaking like a baby)，所以动画片的配音里经常能听到'耶‘

耶，放在句末，表示惊奇/出乎意料，或者感叹。

"耶" is modal particles, which is mostly used in informal situation, like you said, 你们的位子换了耶. In other formal situation, you can also say, "你们的位子换了" P.S. It commonly used in the ancient Chinese prose. e.g. 从耳,邑(右耳旁是“邑”的变形)声。不详) 本义:句末语气词。相当于“吗”或“呢” 例如：岂可近耶 猎虫所耶