Extra security for paper wallets
This is extremely risky and not a good idea.

If you just increment one character, there are only about 50 ways to do that.  It would be extremely easy for an attacker to just try all 50 possibilities, and they would find your key and steal your coins.

Even if you change one character to a new random character, that's only 50 * 58 = 2900 possibilities.  Still very easy.  Particularly since the key has a built-in checksum, so that an attacker can tell with high probability whether their guess is correct with a simple computation.

The security of your private key rests in the fact that it is a random one of an extremely large number of candidates.  By revealing most of the key, you reduce that number of candidates to a very small number, and lose all your security.

Don't reveal any part of your private key, or save it where attackers could get it.  Also, don't try to "encrypt" it with any scheme you come up with by yourself (e.g. a substitution code) - those are also extremely easy to break for any reasonably clever attacker.