So, here’s what I ended up doing. Had to take a hybrid approach since the Key Schedule node can’t handle numeric data.
First, I let the Key Schedule node build or fill in as much data as it can. Even if the Revit schedule has nothing in it, this will populate it.
Next, I collect all the elements that are now in the schedule and set all their values with SetParameterByName.
This seems to work when you have numeric data.
Kudos to @Steven on this post: Key Schedules - non-string data from Excel