You can use "Label Feature" as a trigger. So use this Python label expression:
SR = arcpy.SpatialReference(4326)
lyr = "points"
with arcpy.da.UpdateCursor(lyr,("Shape@","WGSX","WGSy")) as cursor:
for shp,fx,fy in cursor:
newP = shp.projectAs (SR).firstPoint
def FindLabel ( ):
Just modify second line or simply call your layer "points". Also amend X and Y field names in line 3.
I tested it on 500 long dataset and noticed no delay in features redraw with "Label Feature" option ticked. You can even attach this expression to dummy layer with single feature, like shown in picture below:
It's enough to switch this dummy layer on, to trigger calculations on target layer. However script honors selection so either attach it to target, or clear selection on it, when using slave. Use layer properties, to access labeling dialog.