Make AES CBC more secure by destroying each block?
Does it add "more security" [...] flipping a bit (or two) of each AES block and store information about the flips alongside with the key and IV in the RSA encrypted part (so that the recipient can decrypt properly)?


This would essentially be a stream cipher applied to the ciphertext, as a stream cipher encrypts by unpredictably deciding for each bit whether it should be flipped or not.

So this additional scheme can be seen as a custom stream cipher and will most likely add very little security beyond the existing encryption.


  Background of the question is the idea that an attacker, who "sees" the AES encrypted file, needs maybe more time and computing power to run a brute force attack because even when he has the right key and IV the decryption would fail because the blocks are all invalid?


CBC has no notion of "invalid decryption" (beyond padding errors) and so the adversary would have to decide based on the "deciphered" contents whether the decryption was ok or not.