Can you really insert the text you want in one-time pad? The Wikipedia article "One-time pad ~ Authentication" says :


  For example, an attacker who knows that the message contains "meet jane and me tomorrow at three thirty pm" at a particular point can replace that content by any other content of exactly the same length, such as "three thirty meeting is cancelled, stay home", without having access to the one-time pad, a property of all stream ciphers known as malleability.


I don't quite understand how it's possible. 

Let's say the string is encrypted using one-pad time. Hacker somehow gets that encrypted text and he knows that the last word contains 6 chars. So, he removes last 6 chars from the ciphertext and he wants to add his own 6 character word. How he can do that? 

If he just inserts that word, after the decryption that inserted word becomes most likely just gibberish. Or am I wrong?
It is quite simple and stems from the idea that flipping one bit in the ciphertext flips the corresponding bit in the plaintext.

So, say the ciphertext is $1011$ and we know the plaintext is $0101$ (thus the key is $1110$). Say we want a plaintext of $0000$, we just have to change the ciphertext to $1110$ (notice where the bits have been flipped) and we have $1110\oplus 1110=0000$

In that sense you if you can flip any bits you want and you know what the plaintext says and you know what you want the plaintext to say, you flip the right bits in the ciphertext and decryption comes out as you desired.