I'm using a multipolygon PostGIS layer in QGIS 3 and created a rule-based labeling. I'd like to know if when a label is moved by
move label and diagram will it be possible to update the label by changing the entry in the attribute table?
You question is not entirely clear to me, so I cover both options.
Position, by changing coordinates in attribute table?
the label position refers to these coordinate fields in the attribute table.
you are using auxilliary storage for coordinates of label positions. This is the standard setting if you use this tool and didnt change it yourself.
Label, by changing the label value?
Yes, always. Maybe it is necessary to move the canvas a little so the screen gets updated.