Then you should know that attackers don’t take your plain-text or cracked password and the start manually guessing similar codes on your other accounts, unless they are exactly the same. They always need to get a copy of your password (we’ll assume its hashed), then start the guess work using a decoder.
How secure your password is to the program depend on its entropy, which depends on the password’s length and possible characters. Two passwords are either exactly the same or completely different, and not how similar it “looks” to human.
Now, obviously if you make a easy-to-guess scramble (e.g. password123 becomes password123facebook for, well, facebook) then the hacker can do a custom decoder and this does compromise security. There are a lot of little tricks to avoid this, in anycase it will be secure as long as you maintain a high entropy.