hmmm i havent open the editor now but i think that there could be a way to change it, because u know not all races have same amount of getting lumber (nightelf get 5, orcs 10 and later 20 with upgrade i think... and so on) maybe there is a way to change this with gold using the lumber upgrade so u just modify the lumber upgrade and change it to gold if this is possible then use the upgrade before ur game starts or whatever u want to use it... and it should work, maybe there is a way to change it in advanced --> gamplay constants or something like that... good luck !
=)