Are they both correct and intechangeable？
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Are they both correct and interchangeable？
The second one is definitely correct and the "normal" way to say it.
The first one is correct if you punctuate it as 这个布丁很美味,真的, and also if you accept the heavy influence of English sentence structure here because it would then read "This pudding is very delicious, really", which is not the normal way to say it in Chinese.
Interchangeable? Yes I suppose, given the qualification above, and whether you will get any marks in an academic examination for correct arrangements of jumbled-up words is another matter.
1. 这个布丁很美味, 真的. This putin is delicious. Really. 2. 这个布丁真的很美味。 This putin is really delicious.
Sentence 1 is an inverted sentence(倒装句).
Native speakers barely say things in this approach unless intended.
It's enough to understand it but there is no need to say or write in this way unless intended.
(Side story: People in Shangdong province exceptionally like this style)
例子： 在哪里啊，你俩。 真香，这火锅。