What to do when you notice that a value in your paper is wrong, once it is accepted but before it is published?
This is not a major revision. Just change the value in the final version. (And explain to the editor in the cover letter that you are correcting a typo. A misplaced decimal point is essentially a typo.)

You are not misrepresenting yourself in any way. Because you're explaining the change in the cover letter, you are giving the editor the chance to reject the paper if they deem the changes are big enough to count as a "major revision". However, any editor that rejects the paper for that reason would have to be totally insane. Typos get fixed in the final version of papers all the time.