You want to correct the data 'on the form ' . Does that mean you don't want to change the data in the table?
If so then you will have to use an unbound control to display the result.
Use the form current event to do..
If Me.Reason = "Splat" Then
Me.txtModifiedReason= "Splay"
else
Me.txtModifiedReason = me.reason
End If