Similar thing been discuses here: Excel to Revit Key Schedule Help
Problem was mentioned but unresolved.
I’m using Dynamo 126.96.36.199 in Revit 2018.3.
I get following behaviour:
The Key Schedule node is only able to create new key schedule data rows.
If more key schedule data rows already exist, node reduces the number of key schedule data rows to the number of new data rows written in without changing key schedule data.
If more data rows are brought in, only aditional data rows are added (existing key schedule data rows stays unchanged).
The point is to keep updating/maintaining parameters & values outside Revit in Excel.
Imagine that there are a lot of elements already having Key Name values set, but key schedule related parameters - values needs to update for scheduling purposes of the elements.