If you're unsure how to use a memory editor, the way I did it is via Cheat Engine.
Download it, run it, and click the flashing icon. Search for the dwarf fortress process and select it.
Near the bottom right, click the 'add address manually' button. Add the memory address of the exported wealth value and hit OK.
Now, in the far right of the new entry on the bottom that says "0", replace with some big arbitrary value. The moment you hit OK on the new value, it should appear in the DF window where exported wealth is.
Now, the value OP gave didn't work for me, I had 0236F260 as my exported wealth memory address (windows 7 64 bit system). I don't know how reliable it is to give an address like that, since I haven't a clue if they'd be the same for other people.
So! To find yours without a problem, enter your Imported Wealth value into the barabove the "exact value" button. Hit first scan, and you should get a couple of results on the left window pane. Double click those to add them to the bottom area. Now, experimentally change the values by a little bit, watching the Imported wealth value in DF to see which entry is the actual value. Once you've located it (make sure you return any other changed values to their original numbers), left of where the value is, double click the address. Add 8 to the address to get to the exported wealth's address. Remember this value is in hexadecimal, so my final numbers which were ~258 become ~260 when adding 8.
Change the value of this new thing (which should be 0) and the changes should be reflected in DF's exported wealth number.