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.

If you are still in the revision process, changing a single number in the Results section is no problem at all. A simple typo, anywhere in the manuscript, is a minor revision. They will not reject your paper. If worst comes to absolute worst, they will send it back to the referees, but likely that will not happen either.

Just explain the issue to the copy editor or the handling editor - this stuff happens all the time. Don't worry.

Once it has been accepted, things get more difficult, if not impossible to change such stuff.

Once published, an erratum needs to be submitted, which is not a disaster, but does complicate things.

It's just a typo. It's two characters that were swapped. That's all. It's not a massive change that implies a different conclusion. It's the smallest of small changes.

You're clearly competent and have found an error that your peers who reviewed it failed to find. You'll be fine :)