Join Date: May 2004
Location: SIN (LEJ once a year)
Programs: SQ, LH, BA, IHG Diamond AMB, HH Gold, SLH Indulged, Accor Gold, Hyatt Discoverist
Posts: 7,741
You are correct that a simple date change should not incur a mileage top up on or after 24 Jan. As long as no reissue happens and only revalidation.
I would attribute above feedback to maybe too generic info given by the agent. A similar change like what the OP did (stopover adding) would trigger a repricing and cost more miles, just not all changes.