After editing a field or fields in a TXDataWebDataset add a call like MergeChangeLogs (as in TClientDataset) that marks the record as Unchanged so a future call to ApplyUpdates doesn't submit the change.
This is useful when a record has been updated following a call to service which has resulted in a change to the data on the server and the update on the web page is simply to reflect that and does not need to be submitted back.
Hope that makes sense.