I did ask Ignition about that and they say you can change the values in the Historian table that they do not support it and it can break stuff.
"It is possible but highly not recommended as manually managing the tag historian table can break your trends/historian. However, this would be highly complex. To achieve this, you would need to follow how our tag historian works in the back end. The first query retrieves the Gateway and Tag Provider of the tag on the sqlth_drv table. The second query retrieves the scan class in sqlth_scinfo based on your tag in accordance with the first query's result. The third query retrieves all the TE entries that matches your your tagpath along with the scid from the second query. The fourth query retrieves the correct partitions table that matches your window time frame on the sqlth_partitions table. Lastly, the fifth query will look onto the partition table based on the fourth query's result and use the tagid's from the third query to retrieve the data. On the fifth query, you can alter this to instead delete the records that have a value of 'x' to fit your needs."
Others in the Ignition forum said there would be issues. "The query would have to handle history partitioning, etc". "Especially for tags that use analog deadband, as it will scramble the reconstruction of the "compressed" samples."
I was just hoping there may be a way in KEPServerEX to mark the values bad before the Ignition Historian got them. Not something many are looking to do I'm sure.
