The problem with modifying the value 8000, is that you effectively remove sockets from it. 8000 is the socket property, and the number in the next tree (ITEM_PROPERTY_POWERS) is the number of sockets (1065353216 [1.0] for one, 1073741824 [2.0] for two, etc.).
It's better to just ADD the line for evolving weapon. If you add it though, you also need to add another line for the other 3 trees, ITEM_PROPERTY_POWERS needs to be 1065353216, ITEM_PROPERTY_EFFECTID and ITEM_PROPERTY_VFXID must be -1.
Also, the item LEVEL is at index number 16238 (just above SAVEGAME_OBJECT_PLOT)for each item. What that number does, is grow all stats in ITEM_PROPERTY_POWERS by a factor.
Seems to be a lot of fiddly work to get your item to just level with you. I think when I do my first proper play through of DA2 al not be doing that with me items.