Any changes in the regular datafiles will always be wiped out in an update. There is a way around it, make your additions in seperate data and extension files. If you add your add-on in seperate files, they will not be affected when you update (unless you leave the "Delete all files not updated" checkbox checked when you update).
If you are adding things that should be in the data files, then that should be taken up with the WH6 datafile team, in the appropriate forum:
http://support.wolflair.com/index.ph...viewforum&f=26
It is also important to remember that the data files for most game systems (particularly GW games, due to licensing issues) are not written by Lone Wolf themselves, but by volunteers that are not Lone Wolf employees.