Why can't decrypt with OpenSSL if salt changed (for CBC and ECB)
In your command:

openssl enc -aes-256-cbc -in texte -out encrypted_texte -k password


a password is supplied, which will be used to derive the key and IV for encryption. The salt stored in the file is used in conjunction with your password for this purpose. Therefore when you change the salt, you will get both a different IV and a different key in the decryption process, not just the IV. Then you will get problem decrypting in block modes such as CBC and ECB because the padding in the decrypted plaintext will not be correct (decrypted with a wrong key). While in stream modes like CFB, there is no padding, so modifying the salt won't cause a problem, but you will get wrong plaintext back.  

Edit to add: the EVP_BytesToKey() function is used to turn the password and salt into the key and the IV.