In general, I can't think of anything legal that you can do that would mess up std::vector's memory management. std::vector's base structure is intentionally opaque. However, that doesn't mean that there aren't illegal things you can do to mess things up.
There are a number of operations on a std::vector that will invalidate pointers or iterators that refer to a specific element. These are clearly documented.
For example, if you have a pointer to an element of the vector, and you delete that element your pointer is no longer valid.
sure you can. I don't know what could happen if this failed to crash, and went off into undefined land. It usually crashes, but you never know.
oops = 13;
if you are asking if you can corrupt its internal pointers, not easily. There probably is a way. I am sure that if I took a pointer and a union, I can break almost anything with some determination. I could find its size in the raw and mess that up...
If you are using as intended, I would not worry about it.