As such I would say the answer is yes, an affirmation can have a negative tone.

Are affirmations always positive?

What Are Affirmations, and Do They Work? Affirmations are positive statements that can help you to challenge and overcome self-sabotaging and negative thoughts. When you repeat them often, and believe in them, you can start to make positive changes. ... Self-affirmation may also help to mitigate the effects of stress.

Can there be negative affirmations?

Quite simply, if you repeat something often enough you will start to believe it. You may have quite a few negative affirmations running through your head which can change your life in a very bad way. Some of these messages you carry in your head may lead to depression, lack of self esteem and low self confidence.