I'm new here and by no means an expert on cryptography. I like to dabble, and one of my favorite classical ciphers is the Vigenere. I understand that the normal method of Vigenere encrypting is to add the corresponding number of the letter of the key to the number of the letter of the message, thus producing the cipher text for that particular letter. My question is, regardless of key length, is it advantageous to alter the order in which the key is applied to the message? For example, instead of moving forward through the alphabet to obtain the cipher text, what if I started off by going backwards? Or if I alternated by going forward with the first key letter, then backwards with the second, and so on. Or if I alternated by going backward with the first two key letters, then forward with the next two. Would this make it any harder to decipher the message or make it more difficult to use letter frequency analysis to obtain the key?
I can provide examples if my question isn't clear. Thank you in advance for any insight you are able to provide.