I understand the 2019 Railway & Locomotive Historical Society convention is being held in Ogden on May 8-12 to coincide with the sesquicentennial, and the program includes bus transportation to Promontory (Golden Spike National Historic Site) on May 10 for whatever festivities are planned.
2019 R&LHS Convention Information
The R&LHS convention organizers may be able to provide some more details on what's happening and who may be involved. However, since Golden Spike NHS is part of the national park system I assume the lead agency planning the event is the National Park Service itself.
-Philip Marshall