TRichView.com

In OnItemAction(Sender: TCustomRichView; ItemAction: TRVItemAction; Item: TCustomRVItemInfo;
var Text: TRVRawByteString; RVData: TCustomRVData);

the Text is in var, but when ItemAction = rviaInserted, I tried to change the Text, but it does not seems updating the text to my new text.

rviaInserted occurs when the item is already inserted, you cannot modify text in it.
Use rviaInserting.
Please not that this even also happen for all items in the cell when its editing is started and is finished (moving items to a cell inplace editor, and then back)