I agree, but think you are talking about the differences of the NPN and PNP transistors, but I'm talking about the differences of the emisor and the collector in the same transistor.
In a very naive explanation, you can exchange the emisor and the collector, but in a real cirtuit it is a bad idea. (I'm not sure why. I think it may stil work but it's slower or less efficient, but I'm not sure about the details.)
On discrete transistors, they have different sizes, shapes and levels of doping.
On the "old" planar VLSI transistors, nobody even uses the names. They are both built as small as possible and there's no space to fine-tune any of their characteristics. But on some of the new 3D VLSI transistors they are different again.
In a very naive explanation, you can exchange the emisor and the collector, but in a real cirtuit it is a bad idea. (I'm not sure why. I think it may stil work but it's slower or less efficient, but I'm not sure about the details.)