seven unrelated words as passphrase

According to this article
Quote:

https://theintercept.com/2015/03/26/...ers-cant-guess

the human brain has some difficulties to remember seven unrelated words used to form a secure passphrase but can do it with a little practice. In a scenario in which two such passphrases are necessary, it seems that remembering 2 passphrases becomes exponentially more difficult.

Being no expert in security, I thought that a user could learn to remember 7 words of a passphrase supposed to be unbreakable and modify them to create a second passphrase. Examples:
Quote:

passphrase 1: cult paoli pal finn juice onward ross passphrase 2: cultm paolii palc finnh juicea onwarde rossl

The letters of the word "michael" having been used to add 1 letter to each word, the extra thing to remember would only be how each of the 7 words have been modified.
Although there could be some sort of predictability and loss of entropy in such practice, I can not see how.

My question: would such modification of the words affect negatively the security of the modified passphrase and how?

Any hint welcome.

Thank you for your help.