When you use keynotes and realize you need to revise existing keynote information it easy to change what the keynote text value is. We just need to edit the existing information and reload the keynote file.
It's a little different situation when you decide you need to change the numbering that is already in play. It's no problem if you are just shuffling note information around so you get the numbering sequence you prefer. As long as the keynote value remains in the list Revit will find it. You just need to make sure that any elements that are supposed to carry a certain keynote value still do after you shuffle them.
However, if you revise things and introduce a new numbering scheme and reload the file you'll find the keynotes will get confused. They stop displaying the correct information. For example let's say the keynote that was number 1 is now the letter A. There isn't a separate GUID that is guiding this alignment of data, Revit is relying on the information in the text file entirely. So Revit doesn't find the number 1 anymore and can't pair up the keynote value and keynote text anymore. The tag just reports 1 since that's what was stored to begin with.
The best place to check and revise the keynote assignment after revising numbers is in the keynote legend. You'll be able to review each keynote and activate the keynote table via the Keynote Value parameter, the little browse button that appears when you click on the value in the schedule.
You can select each confused keynote and map it to the correct keynote value. Once you've revisited all of the affected keynotes in the legend you'll find that the keynote tags throughout the documentation will show the correct information again.