If you drag a dimension string, the texts will re-center themselves on their segments, assuming the texts have not been moved manually.
You don't actually have to drag the string anywhere, just a drag and a double-click will do it.
The only way a dim text would be off center without you moving it is if you customized the text.
Who cares? You, because you probably changed some texts to read EQ or something, and re-centering them by hand is a cumulative chore.
So, after changing the texts to read whatever, (deselect the texts,) select the string, Cmd+D, clickclick. Note: if the dimension tool is active (very likely), you have to do a Drag command; cursor-drag will edit the witness line length. You can drag with the arrow tool and it works; I think the Cmd+D method is better since you don't have to be precise. Any texts that you moved manually will stay put. AC remembers which those are.
I just dimensioned all the Vassos ceiling lights on the electrical plan, which, if you've never had the pleasure, boils down to a LOT of EQ EQ EQ EQ EQ. So I was really happy with this discovery.
Sort of cross-posted here.